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dialect improuvments - #62
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DdlGenerator gains commentOnTable(table, comment) and commentOnColumn(table, column, comment, currentMeta). The default is the SQL-standard COMMENT ON … IS '…' (a null comment removes it with IS NULL); both return Optional so a dialect can say it has no comments. Overrides: - MySQL/MariaDB: ALTER TABLE t COMMENT = '…'; a column comment can only be set by restating the column (MODIFY COLUMN c <type> [NOT NULL] [DEFAULT d] COMMENT '…'), hence the currentMeta parameter. - SQL Server: the MS_Description extended property — update when present, add otherwise, drop for null (schema defaults to dbo). - Oracle: IS '' instead of IS NULL. - ClickHouse: ALTER TABLE t MODIFY COMMENT / COMMENT COLUMN. - Hive: table comment via TBLPROPERTIES; no column comment. - Derby, SQLite: no comments (empty).
Oracle accepts ON DELETE CASCADE and ON DELETE SET NULL only. NO ACTION is the implicit behavior; RESTRICT and SET DEFAULT do not exist and fail with ORA-02000.
ALTER INDEX qualifies the index with the table's schema; SQL Server's sp_rename addresses a constraint as schema.constraint, not schema.table.constraint.
createTable dropped the primary key's constraint name, so every database picked its own and a later rename or drop by the modelled name missed. The key is now written as CONSTRAINT name PRIMARY KEY (…) when it has a name. ClickHouse and Hive/Impala have no named table constraints and keep the unnamed form (supportsNamedPrimaryKey).
Signed-off-by: <bulahovdenis@gmail.com>
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