The following table lists the associations between individual SQL DML statements and lock upgrades and downgrades at the row (rowkey or rowhash), view, base table, and database object levels:
| LOCKING Modifier Severity | SQL DML Statements |
|---|---|
| EXCLUSIVE or WRITE |
|
| READ or SHARE | SELECT |
| ACCESS | SELECT |
| ACCESS for LOAD COMMITTED | SELECT |
EXCLUSIVE and WRITE are the only lock severities for the DELETE, INSERT, MERGE, UPDATE, and SELECT AND CONSUME statements because the default lock severity for these statements is WRITE. You cannot downgrade a WRITE lock for these statements because doing so would compromise the integrity of the database. Because the SELECT statement does not change data, and therefore cannot compromise database integrity, you are permitted to change its default locking severity to any other severity.
You can specify lower locking severity levels than are listed in this table, but if you do, the system ignores them and uses WRITE.
For details about locking levels, locking severities, and the relationship between them, see Teradata Vantage™ - SQL Request and Transaction Processing, B035-1142.