SQL · Theory

BEFORE UPDATE Trigger

Theory

89/439

BEFORE UPDATE Trigger

BEFORE UPDATE Trigger (BEFORE_UPDATE_TRIGGER) is a MySQL date/time helper. Dates are stored in DATE / DATETIME / TIMESTAMP columns. Always quote literals: '2026-08-19'.

Typical pattern: SELECT BEFORE_UPDATE_TRIGGER(…); or SELECT BEFORE_UPDATE_TRIGGER(dob) FROM students; NOW() / CURDATE() / CURTIME() have empty brackets — they read the clock.

DATE_FORMAT(dob, '%d-%b-%Y') is for display. DATEDIFF(end, start) is days between. INTERVAL 7 DAY is how you add a week: DATE_ADD(CURDATE(), INTERVAL 7 DAY).

Trap: comparing dates as VARCHAR. Trap: TIMESTAMP vs DATETIME timezone stories — DATETIME is ‘wall clock’, TIMESTAMP is UTC-stored (say this only if asked).

On the example next to this theory — BEFORE UPDATE Trigger — uPDATE changes existing rows — always scope with WHERE.

Exam tip

BEFORE_UPDATE_TRIGGER: one SELECT example. Quote 'YYYY-MM-DD'.

BEFORE UPDATE Trigger — sample query

CREATE TABLE products (id INTEGER PRIMARY KEY, name TEXT, price REAL);
INSERT INTO products VALUES (1, 'Mouse', 499);
UPDATE products SET price = 449 WHERE id = 1;
SELECT * FROM products;

BEFORE UPDATE Trigger — uPDATE changes existing rows — always scope with WHERE.

Short notes

DefBEFORE_UPDATE_TRIGGER works on DATE/DATETIME values.
RuleQuote date literals. NOW() for current datetime.
TrapDates as strings without a real DATE column.

SQL · Theory

BEFORE UPDATE Trigger

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Theory

89/439

BEFORE UPDATE Trigger

BEFORE UPDATE Trigger (BEFORE_UPDATE_TRIGGER) is a MySQL date/time helper. Dates are stored in DATE / DATETIME / TIMESTAMP columns. Always quote literals: '2026-08-19'.

Typical pattern: SELECT BEFORE_UPDATE_TRIGGER(…); or SELECT BEFORE_UPDATE_TRIGGER(dob) FROM students; NOW() / CURDATE() / CURTIME() have empty brackets — they read the clock.

DATE_FORMAT(dob, '%d-%b-%Y') is for display. DATEDIFF(end, start) is days between. INTERVAL 7 DAY is how you add a week: DATE_ADD(CURDATE(), INTERVAL 7 DAY).

Trap: comparing dates as VARCHAR. Trap: TIMESTAMP vs DATETIME timezone stories — DATETIME is ‘wall clock’, TIMESTAMP is UTC-stored (say this only if asked).

On the example next to this theory — BEFORE UPDATE Trigger — uPDATE changes existing rows — always scope with WHERE.

Exam tip

BEFORE_UPDATE_TRIGGER: one SELECT example. Quote 'YYYY-MM-DD'.

BEFORE UPDATE Trigger — sample query

CREATE TABLE products (id INTEGER PRIMARY KEY, name TEXT, price REAL);
INSERT INTO products VALUES (1, 'Mouse', 499);
UPDATE products SET price = 449 WHERE id = 1;
SELECT * FROM products;

BEFORE UPDATE Trigger — uPDATE changes existing rows — always scope with WHERE.

Short notes

DefBEFORE_UPDATE_TRIGGER works on DATE/DATETIME values.
RuleQuote date literals. NOW() for current datetime.
TrapDates as strings without a real DATE column.

BEFORE UPDATE Trigger

BEFORE UPDATE Trigger — sample query

Short notes

Questions

BEFORE UPDATE Trigger

BEFORE UPDATE Trigger — sample query

Short notes

Questions