/aurora-dsql

MySQL to DSQL: Structural Changes

Part of MySQL to DSQL DDL Migration. See Common Verify & Swap Pattern for the shared migration end-pattern.

ADD/DROP CONSTRAINT Migration

MySQL syntax:

ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column_name);
ALTER TABLE table_name ADD CONSTRAINT constraint_name CHECK (condition);
ALTER TABLE table_name DROP CONSTRAINT constraint_name;
-- or MySQL-specific:
ALTER TABLE table_name DROP INDEX index_name;
ALTER TABLE table_name DROP CHECK constraint_name;

DSQL: MUST use Table Recreation Pattern.

Pre-Migration Validation (for ADD CONSTRAINT)

MUST validate existing data satisfies the new constraint.

-- For UNIQUE constraint: check for duplicates
SELECT target_column, COUNT(*) as cnt FROM target_table
GROUP BY target_column HAVING COUNT(*) > 1 LIMIT 10;
-- MUST ABORT if any duplicates exist

-- For CHECK constraint: validate all rows pass
SELECT COUNT(*) as invalid_count FROM target_table
WHERE NOT (check_condition);
-- MUST ABORT if invalid_count > 0

Migration Steps (ADD CONSTRAINT)

Step 1: Create new table with the constraint

CREATE TABLE target_table_new (
  id UUID PRIMARY KEY,
  email VARCHAR(255) UNIQUE,  -- Added UNIQUE constraint
  age INTEGER CHECK (age >= 0),  -- Added CHECK constraint
  other_column TEXT
);

Step 2: Copy data

INSERT INTO target_table_new (id, email, age, other_column)
SELECT id, email, age, other_column
FROM target_table;

Step 3: Verify and swap (see Common Pattern)

Migration Steps (DROP CONSTRAINT)

Step 1: Identify existing constraints

SELECT constraint_name, constraint_type
FROM information_schema.table_constraints
WHERE table_name = 'target_table'
   AND constraint_type IN ('UNIQUE', 'CHECK');

Step 2: Create new table without the constraint

CREATE TABLE target_table_new (
  id UUID PRIMARY KEY,
  email VARCHAR(255),  -- Removed UNIQUE constraint
  other_column TEXT
);

Step 3: Copy data

INSERT INTO target_table_new (id, email, other_column)
SELECT id, email, other_column
FROM target_table;

Step 4: Verify and swap (see Common Pattern)

MODIFY PRIMARY KEY Migration

MySQL syntax:

ALTER TABLE table_name DROP PRIMARY KEY, ADD PRIMARY KEY (new_column);

DSQL: MUST use Table Recreation Pattern.

Pre-Migration Validation

MUST validate new PK column has unique, non-null values.

-- Check for duplicates
SELECT new_pk_column, COUNT(*) as cnt FROM target_table
GROUP BY new_pk_column HAVING COUNT(*) > 1 LIMIT 10;
-- MUST ABORT if any duplicates exist

-- Check for NULLs
SELECT COUNT(*) as null_count FROM target_table
WHERE new_pk_column IS NULL;
-- MUST ABORT if null_count > 0

Migration Steps

Step 1: Create new table with new primary key

CREATE TABLE target_table_new (
  new_pk_column UUID PRIMARY KEY,  -- New PK
  old_pk_column VARCHAR(255),      -- Demoted to regular column
  other_column TEXT
);

Step 2: Copy data

INSERT INTO target_table_new (new_pk_column, old_pk_column, other_column)
SELECT new_pk_column, old_pk_column, other_column
FROM target_table;

Step 3: Verify and swap (see Common Pattern)