docs: add mysql 1452 | pg 57p01 (#1066)

* add mysql 1452 | pg 57p01

* Update content/reference/mysql/error/1452-cannot-add-child-row.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update content/reference/postgres/error/57p01-admin-shutdown-postgres.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* fix

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: adela-bytebase

content/reference/mysql/error/1452-cannot-add-child-row.md

@@ -0,0 +1,186 @@
+---
+title: 'ERROR 1452 (23000): Cannot Add or Update a Child Row in MySQL'
+---
+
+## Error Message
+
+```sql
+ERROR 1452 (23000): Cannot add or update a child row:
+a foreign key constraint fails (`mydb`.`orders`, CONSTRAINT `fk_orders_customer`
+FOREIGN KEY (`customer_id`) REFERENCES `customers` (`id`))
+```
+
+Other common variations:
+
+```sql
+ERROR 1452 (23000): Cannot add or update a child row:
+a foreign key constraint fails (`mydb`.`order_items`, CONSTRAINT `fk_items_order`
+FOREIGN KEY (`order_id`) REFERENCES `orders` (`id`) ON DELETE CASCADE)
+```
+
+## What Triggers This Error
+
+MySQL 1452 fires when an INSERT or UPDATE tries to set a foreign key column to a value that doesn't exist in the referenced parent table. The fix depends on why the parent row is missing or unmatched:
+
+- **Parent row doesn't exist** — inserting a FK value with no matching row in the parent table
+- **Data type mismatch** — FK column and referenced column have different types (INT vs BIGINT, signed vs unsigned)
+- **Character set or collation mismatch** — parent and child columns use different character sets
+- **Self-referencing foreign key** — inserting a row that references itself or a not-yet-inserted row
+- **Bulk import with wrong insertion order** — child rows loaded before parent rows
+
+## Fix by Scenario
+
+### Parent row doesn't exist
+
+The most common cause. You're inserting a row with a `customer_id` of 42, but there's no customer with `id = 42` in the parent table.
+
+```sql
+-- Check if the referenced parent row exists
+SELECT id FROM customers WHERE id = 42;
+-- Empty result = that's your problem
+
+-- Option 1: insert the parent row first
+INSERT INTO customers (id, name) VALUES (42, 'Acme Corp');
+INSERT INTO orders (customer_id, total) VALUES (42, 99.99);
+
+-- Option 2: if the parent was deleted, check if it's expected
+-- Maybe the application should use ON DELETE SET NULL instead of RESTRICT
+```
+
+If parent rows are frequently missing due to race conditions in concurrent inserts, wrap the parent + child inserts in a single transaction:
+
+```sql
+START TRANSACTION;
+INSERT INTO customers (id, name) VALUES (42, 'Acme Corp');
+INSERT INTO orders (customer_id, total) VALUES (42, 99.99);
+COMMIT;
+```
+
+### Data type mismatch between FK columns
+
+The FK column and the referenced column must have the exact same data type. A common trap: `INT UNSIGNED` in the parent vs `INT` (signed) in the child, or `INT` vs `BIGINT`.
+
+```sql
+-- Check column types for both tables
+SELECT TABLE_NAME, COLUMN_NAME, COLUMN_TYPE
+FROM information_schema.COLUMNS
+WHERE TABLE_SCHEMA = 'mydb'
+  AND ((TABLE_NAME = 'customers' AND COLUMN_NAME = 'id')
+    OR (TABLE_NAME = 'orders' AND COLUMN_NAME = 'customer_id'));
+
+-- Example output showing the mismatch:
+-- customers | id          | int unsigned
+-- orders    | customer_id | int          <-- signed vs unsigned
+```
+
+**Fix:** Alter the child column to match the parent exactly:
+
+```sql
+-- Drop the FK, fix the type, re-add the FK
+ALTER TABLE orders DROP FOREIGN KEY fk_orders_customer;
+ALTER TABLE orders MODIFY customer_id INT UNSIGNED NOT NULL;
+ALTER TABLE orders ADD CONSTRAINT fk_orders_customer
+  FOREIGN KEY (customer_id) REFERENCES customers(id);
+```
+
+### Character set or collation mismatch
+
+For string-type foreign keys (e.g., `VARCHAR` codes), both columns must use the same character set and collation. A `utf8mb4` parent with a `utf8` child will fail.
+
+```sql
+-- Check character set and collation for both columns
+SELECT TABLE_NAME, COLUMN_NAME, CHARACTER_SET_NAME, COLLATION_NAME
+FROM information_schema.COLUMNS
+WHERE TABLE_SCHEMA = 'mydb'
+  AND COLUMN_NAME IN ('country_code')
+  AND TABLE_NAME IN ('countries', 'addresses');
+
+-- Example mismatch:
+-- countries | country_code | utf8mb4 | utf8mb4_general_ci
+-- addresses | country_code | utf8    | utf8_general_ci
+```
+
+**Fix:**
+
+```sql
+ALTER TABLE addresses DROP FOREIGN KEY fk_addresses_country;
+ALTER TABLE addresses MODIFY country_code VARCHAR(3)
+  CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL;
+ALTER TABLE addresses ADD CONSTRAINT fk_addresses_country
+  FOREIGN KEY (country_code) REFERENCES countries(country_code);
+```
+
+### Self-referencing foreign key
+
+A table that references itself (e.g., an `employees` table with `manager_id` → `id`). The first row fails because there's no parent row yet.
+
+```sql
+-- This fails: manager_id=1 doesn't exist yet
+INSERT INTO employees (id, name, manager_id) VALUES (1, 'CEO', 1);
+
+-- ERROR 1452: Cannot add or update a child row
+```
+
+**Fix:** Insert the root row with `NULL` for the self-reference, then update it:
+
+```sql
+-- Option 1: allow NULL for the root
+INSERT INTO employees (id, name, manager_id) VALUES (1, 'CEO', NULL);
+
+-- Option 2: temporarily disable FK checks (use with caution)
+SET FOREIGN_KEY_CHECKS = 0;
+INSERT INTO employees (id, name, manager_id) VALUES (1, 'CEO', 1);
+SET FOREIGN_KEY_CHECKS = 1;
+```
+
+For hierarchical data, it's common practice to allow `NULL` on the self-referencing FK to represent the root node.
+
+### Bulk import with wrong insertion order
+
+When loading data from a dump or CSV, child table rows loaded before their parent rows will fail. This is the most common cause during migrations.
+
+```sql
+-- This fails because orders references customers, but customers isn't loaded yet
+LOAD DATA INFILE 'orders.csv' INTO TABLE orders;
+
+-- ERROR 1452: Cannot add or update a child row
+```
+
+**Fix:**
+
+```sql
+-- Option 1: load tables in dependency order
+LOAD DATA INFILE 'customers.csv' INTO TABLE customers;
+LOAD DATA INFILE 'orders.csv' INTO TABLE orders;
+LOAD DATA INFILE 'order_items.csv' INTO TABLE order_items;
+
+-- Option 2: disable FK checks during the entire import
+SET FOREIGN_KEY_CHECKS = 0;
+LOAD DATA INFILE 'order_items.csv' INTO TABLE order_items;
+LOAD DATA INFILE 'orders.csv' INTO TABLE orders;
+LOAD DATA INFILE 'customers.csv' INTO TABLE customers;
+SET FOREIGN_KEY_CHECKS = 1;
+
+-- IMPORTANT: verify data integrity after re-enabling
+-- Find orphaned child rows
+SELECT o.id, o.customer_id
+FROM orders o
+LEFT JOIN customers c ON o.customer_id = c.id
+WHERE c.id IS NULL;
+```
+
+`mysqldump` handles this automatically by adding `SET FOREIGN_KEY_CHECKS = 0` at the top of the dump file.
+
+## Prevention
+
+- Always insert parent rows before child rows — enforce this in your application's data layer
+- Use consistent data types for FK columns — prefer `BIGINT UNSIGNED` for all ID columns across the schema
+- Standardize on `utf8mb4` and a single collation across all tables
+- When writing migration scripts, order the inserts by table dependency (parents first)
+- After bulk imports with `FOREIGN_KEY_CHECKS = 0`, always run integrity checks to find orphaned rows
+
+<HintBlock type="info">
+
+Bytebase's [SQL Review](https://docs.bytebase.com/sql-review/review-rules/) can enforce consistent column types across foreign key relationships during schema change review. See also [ERROR 1451: Cannot Delete or Update a Parent Row](/reference/mysql/error/1451-cannot-delete-parent-row) for the reverse direction (deleting a parent that has children).
+
+</HintBlock>