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feat: support ClickHouse COLUMNS(...) APPLY/EXCEPT/REPLACE transformers (#2631) (#2635)
* feat(parser): support ClickHouse COLUMNS(...) APPLY/EXCEPT/REPLACE transformers Adds a dedicated select-item branch for a COLUMNS('regexp') matcher followed by one or more transformers, fixing #2631 (APPLY with a lambda such as x -> round(x, 2) failed to parse; without a lambda, APPLY(...) was silently mis-parsed as the select item alias). - new ColumnsExpression / ColumnsTransformer AST nodes with an ordered transformer list, since ClickHouse parses transformers in a loop (they may repeat and combine in any order) - semantic lookahead isColumnsExpressionAhead() keeps a plain COLUMNS('regexp') on the regular Function path - expression visitor, adapter, deparser, validator and TablesNamesFinder traverse the new node Signed-off-by: 付典 <fudianchn@gmail.com> * fix(parser): add default case to the ColumnsTransformer type switch Satisfies the PMD exhaustive-switch rule (Codacy '1 new issue') and fails loudly if a future ColumnsTransformerType constant is added without updating appendTo; unreachable for the current APPLY/EXCEPT/REPLACE constants, so behavior is unchanged. Same pattern as JsonFunction's Unhandled JsonOnResponseBehavior guard. Signed-off-by: 付典 <fudianchn@gmail.com> * fix: preserve COLUMNS traversal and alias boundaries Reuse alias grammar at each transformer boundary, preserve JJTree parents and lookahead visibility, and route all child expressions through visitor hooks. Add consumer and grammar regression coverage. Signed-off-by: 付典 <fudianchn@gmail.com> * style: use simple name for the Addition cast in ColumnsExpressionTest The fully qualified name trips the UnnecessaryFullyQualifiedName code style check. Import the type instead, matching the sibling ExpressionPrecedenceTest. Signed-off-by: 付典 <fudianchn@gmail.com> --------- Signed-off-by: 付典 <fudianchn@gmail.com>
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‎README.md‎

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@@ -140,6 +140,7 @@ and missing syntax gets added on demand — [open an issue](https://github.com/J
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|---|---|
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| **Queries** | `SELECT` · `WITH …` · Piped SQL |
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| **ksqlDB windows** | JOIN `WITHIN`, window `GRACE PERIOD`, and `EMIT CHANGES`/`FINAL` |
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| **ClickHouse column selection** | `COLUMNS('regexp')` select items with chained `APPLY`, `EXCEPT`, and `REPLACE` transformers |
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| **DML** | `INSERT` · `UPDATE` · `UPSERT` · `MERGE` · `DELETE` · `TRUNCATE TABLE` |
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| **DDL** | `CREATE …` · `ALTER …` · `DROP …` |
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| **PostgreSQL RLS** | `CREATE POLICY` · `ALTER TABLE … ENABLE`/`DISABLE`/`FORCE`/`NO FORCE ROW LEVEL SECURITY` |

‎src/main/java/net/sf/jsqlparser/expression/ColumnsExpression.java‎

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/*-
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* #%L
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* JSQLParser library
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* %%
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* Copyright (C) 2004 - 2026 JSQLParser
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* %%
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* Dual licensed under GNU LGPL 2.1 or Apache License 2.0
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* #L%
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*/
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package net.sf.jsqlparser.expression;
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import java.util.ArrayList;
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import java.util.List;
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import net.sf.jsqlparser.parser.ASTNodeAccessImpl;
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/**
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* A ClickHouse {@code COLUMNS('regexp')} matcher with one or more transformers, for example
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* {@code COLUMNS('^metric_') APPLY(x -> round(x, 2))}.
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*
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* Without a transformer, {@code COLUMNS('regexp')} keeps parsing as a regular
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* {@link net.sf.jsqlparser.expression.Function}.
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*/
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public class ColumnsExpression extends ASTNodeAccessImpl implements Expression {
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private Expression columns;
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private List<ColumnsTransformer> transformers;
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public ColumnsExpression(Expression columns) {
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this.columns = columns;
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this.transformers = new ArrayList<>();
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}
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public ColumnsExpression(Expression columns, List<ColumnsTransformer> transformers) {
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this.columns = columns;
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this.transformers = transformers;
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}
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public Expression getColumns() {
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return columns;
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}
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public ColumnsExpression setColumns(Expression columns) {
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this.columns = columns;
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return this;
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}
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public List<ColumnsTransformer> getTransformers() {
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return transformers;
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}
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public ColumnsExpression setTransformers(List<ColumnsTransformer> transformers) {
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this.transformers = transformers;
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return this;
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}
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public List<Expression> getAllExpressions() {
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List<Expression> expressions = new ArrayList<>();
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if (columns != null) {
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expressions.add(columns);
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}
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for (ColumnsTransformer transformer : transformers) {
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transformer.collectExpressions(expressions);
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}
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return expressions;
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}
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public StringBuilder appendTo(StringBuilder builder) {
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builder.append(columns);
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for (ColumnsTransformer transformer : transformers) {
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builder.append(" ").append(transformer);
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}
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return builder;
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}
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@Override
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public String toString() {
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return appendTo(new StringBuilder()).toString();
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}
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@Override
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public <T, S> T accept(ExpressionVisitor<T> expressionVisitor, S context) {
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return expressionVisitor.visit(this, context);
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}
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}

‎src/main/java/net/sf/jsqlparser/expression/ColumnsTransformer.java‎

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/*-
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* #%L
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* JSQLParser library
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* %%
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* Copyright (C) 2004 - 2026 JSQLParser
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* %%
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* Dual licensed under GNU LGPL 2.1 or Apache License 2.0
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* #L%
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*/
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package net.sf.jsqlparser.expression;
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import java.util.List;
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import net.sf.jsqlparser.expression.operators.relational.ParenthesedExpressionList;
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import net.sf.jsqlparser.parser.ASTNodeAccessImpl;
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import net.sf.jsqlparser.schema.Column;
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import net.sf.jsqlparser.statement.select.Select;
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import net.sf.jsqlparser.statement.select.SelectItem;
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/**
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* A ClickHouse transformer following a {@code COLUMNS(...)} matcher, for example the
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* {@code APPLY(x -> round(x, 2))} in {@code SELECT COLUMNS('^m') APPLY(x -> round(x, 2))}.
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*
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* ClickHouse parses its transformers in a loop, so they may repeat and combine in any order.
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*/
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public class ColumnsTransformer extends ASTNodeAccessImpl {
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public enum ColumnsTransformerType {
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APPLY, EXCEPT, REPLACE
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}
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private ColumnsTransformerType type;
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private Expression applyExpression;
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private ParenthesedExpressionList<Column> exceptColumns;
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private List<SelectItem<?>> replaceItems;
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public ColumnsTransformer(ColumnsTransformerType type) {
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this.type = type;
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}
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public ColumnsTransformerType getType() {
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return type;
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}
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public ColumnsTransformer setType(ColumnsTransformerType type) {
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this.type = type;
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return this;
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}
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public Expression getApplyExpression() {
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return applyExpression;
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}
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public ColumnsTransformer setApplyExpression(Expression applyExpression) {
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this.applyExpression = applyExpression;
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return this;
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}
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public ParenthesedExpressionList<Column> getExceptColumns() {
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return exceptColumns;
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}
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public ColumnsTransformer setExceptColumns(ParenthesedExpressionList<Column> exceptColumns) {
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this.exceptColumns = exceptColumns;
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return this;
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}
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public List<SelectItem<?>> getReplaceItems() {
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return replaceItems;
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}
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public ColumnsTransformer setReplaceItems(List<SelectItem<?>> replaceItems) {
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this.replaceItems = replaceItems;
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return this;
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}
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void collectExpressions(List<Expression> expressions) {
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switch (type) {
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case APPLY:
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if (applyExpression != null) {
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expressions.add(applyExpression);
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}
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break;
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case EXCEPT:
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if (exceptColumns != null) {
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expressions.addAll(exceptColumns);
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}
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break;
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case REPLACE:
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if (replaceItems != null) {
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for (SelectItem<?> item : replaceItems) {
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expressions.add(item.getExpression());
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}
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}
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break;
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default:
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throw new IllegalStateException("Unhandled ColumnsTransformerType: " + type);
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}
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}
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public StringBuilder appendTo(StringBuilder builder) {
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switch (type) {
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case APPLY:
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builder.append("APPLY(").append(applyExpression).append(")");
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break;
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case EXCEPT:
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builder.append("EXCEPT ").append(exceptColumns);
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break;
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case REPLACE:
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builder.append("REPLACE(").append(Select.getStringList(replaceItems)).append(")");
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break;
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default:
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throw new IllegalStateException("Unhandled ColumnsTransformerType: " + type);
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}
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return builder;
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}
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@Override
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public String toString() {
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return appendTo(new StringBuilder()).toString();
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}
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}

‎src/main/java/net/sf/jsqlparser/expression/ExpressionVisitor.java‎

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this.visit(lambdaExpression, null);
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}
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default <S> T visit(ColumnsExpression columnsExpression, S context) {
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for (Expression expression : columnsExpression.getAllExpressions()) {
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if (expression != null) {
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expression.accept(this, context);
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}
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}
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return null;
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}
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default void visit(ColumnsExpression columnsExpression) {
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this.visit(columnsExpression, null);
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}
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<S> T visit(HighExpression highExpression, S context);
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default void visit(HighExpression highExpression) {

‎src/main/java/net/sf/jsqlparser/expression/ExpressionVisitorAdapter.java‎

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return lambdaExpression.getExpression().accept(this, context);
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}
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@Override
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public <S> T visit(ColumnsExpression columnsExpression, S context) {
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return visitExpressions(columnsExpression, context, columnsExpression.getAllExpressions());
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}
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@Override
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public <S> T visit(HighExpression highExpression, S context) {
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return highExpression.getExpression().accept(this, context);

‎src/main/java/net/sf/jsqlparser/util/TablesNamesFinder.java‎

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return null;
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}
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@Override
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public <S> Void visit(ColumnsExpression columnsExpression, S context) {
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for (Expression expression : columnsExpression.getAllExpressions()) {
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if (expression != null) {
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expression.accept(this, context);
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}
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}
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return null;
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}
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@Override
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public <S> Void visit(HighExpression highExpression, S context) {
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highExpression.getExpression().accept(this, context);

‎src/main/java/net/sf/jsqlparser/util/deparser/ExpressionDeParser.java‎

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import net.sf.jsqlparser.expression.CaseExpression;
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import net.sf.jsqlparser.expression.CastExpression;
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import net.sf.jsqlparser.expression.CollateExpression;
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import net.sf.jsqlparser.expression.ColumnsExpression;
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import net.sf.jsqlparser.expression.ColumnsTransformer;
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import net.sf.jsqlparser.expression.ConnectByPriorOperator;
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import net.sf.jsqlparser.expression.ConnectByRootOperator;
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import net.sf.jsqlparser.expression.DateTimeLiteralExpression;
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return builder;
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}
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@Override
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public <S> StringBuilder visit(ColumnsExpression columnsExpression, S context) {
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columnsExpression.getColumns().accept(this, context);
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for (ColumnsTransformer transformer : columnsExpression.getTransformers()) {
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switch (transformer.getType()) {
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case APPLY:
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builder.append(" APPLY(");
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transformer.getApplyExpression().accept(this, context);
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builder.append(")");
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break;
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case EXCEPT:
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builder.append(" EXCEPT ");
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transformer.getExceptColumns().accept(this, context);
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break;
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case REPLACE:
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builder.append(" REPLACE(");
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boolean first = true;
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for (SelectItem<?> item : transformer.getReplaceItems()) {
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if (!first) {
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builder.append(", ");
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}
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first = false;
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item.getExpression().accept(this, context);
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if (item.getAlias() != null) {
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builder.append(item.getAlias());
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}
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}
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builder.append(")");
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break;
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default:
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throw new IllegalStateException(
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"Unhandled ColumnsTransformerType: " + transformer.getType());
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}
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}
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return builder;
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}
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@Override
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public <S> StringBuilder visit(HighExpression highExpression, S context) {
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return builder.append(highExpression.toString());

‎src/main/java/net/sf/jsqlparser/util/validation/validator/ExpressionValidator.java‎

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import net.sf.jsqlparser.expression.CaseExpression;
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import net.sf.jsqlparser.expression.CastExpression;
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import net.sf.jsqlparser.expression.CollateExpression;
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import net.sf.jsqlparser.expression.ColumnsExpression;
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import net.sf.jsqlparser.expression.ConnectByPriorOperator;
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import net.sf.jsqlparser.expression.ConnectByRootOperator;
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import net.sf.jsqlparser.expression.DateTimeLiteralExpression;
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return null;
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}
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@Override
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public <S> Void visit(ColumnsExpression columnsExpression, S context) {
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for (Expression expression : columnsExpression.getAllExpressions()) {
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if (expression != null) {
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expression.accept(this, context);
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}
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}
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return null;
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}
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@Override
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public <S> Void visit(HighExpression highExpression, S context) {
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highExpression.getExpression().accept(this, context);

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