UPDATE
In MySQL, UPDATE allows the following keywords: LOW_PRIORITY, ORDER BY, LIMIT, and IGNORE.
LOW_PRIORITY
With the LOW_PRIORITY modifier, execution of UPDATE is delayed.
Input
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# LOW_PRIORITY UPDATE LOW_PRIORITY employees SET department_id=2; |
Output
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-- LOW_PRIORITY UPDATE "public"."employees" SET "department_id" = 2; |
ORDER BY
In MySQL, if an UPDATE statement includes an ORDER BY clause, the rows will be updated in the order specified by the clause.
Input
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# ORDER BY UPDATE employees SET department_id=department_id+1 ORDER BY id; |
Output
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-- ORDER BY UPDATE "public"."employees" SET "department_id" = department_id+1; |
LIMIT
UPDATE LIMIT syntax can be used to limit the scope. A clause is a limit on row matching. As long as the rows that satisfy the clause are found, the statements will stop, regardless of whether they have actually changed.
Input
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# LIMIT UPDATE employees SET department_id=department_id+1 LIMIT 3 ; UPDATE employees SET department_id=department_id+1 LIMIT 3 , 10 ; # LIMIT + OFFSET UPDATE employees SET department_id=department_id+1 LIMIT 3 OFFSET 2; # LIMIT + ORDER BY UPDATE employees SET department_id=department_id+1 ORDER BY fname LIMIT 3 ; # LIMIT + WHERE + ORDER BY UPDATE employees SET department_id=department_id+1 WHERE id<5 ORDER BY fname LIMIT 3 ; # LIMIT + WHERE + ORDER BY + OFFSET UPDATE employees SET department_id=department_id+1 WHERE id<5 ORDER BY fname LIMIT 3 OFFSET 2 ; |
Output
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-- LIMIT UPDATE "public"."employees" SET "department_id" = department_id+1; UPDATE "public"."employees" SET "department_id" = department_id+1; -- LIMIT + OFFSET UPDATE "public"."employees" SET "department_id" = department_id+1; -- LIMIT + ORDER BY UPDATE "public"."employees" SET "department_id" = department_id+1; -- LIMIT + WHERE + ORDER BY UPDATE "public"."employees" SET "department_id" = department_id+1 WHERE id<5; -- LIMIT + WHERE + ORDER BY + OFFSET UPDATE "public"."employees" SET "department_id" = department_id+1 WHERE id<5; |
IGNORE
With the IGNORE modifier, the UPDATE statement does not abort even if errors occur during execution.
Input
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# IGNORE UPDATE IGNORE employees SET department_id=3; |
Output
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-- IGNORE UPDATE "public"."employees" SET "department_id" = 3; |
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