SQL · Theory

IF()

Theory

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IF()

IF(condition, a, b) is a function: IF(marks >= 40, 'Pass', 'Fail'). CASE is clearer for many branches. IF as a procedure statement (IF THEN END IF) is different — that is flow control inside stored programs.

Trap — mixing IF() function with procedural IF. Trap: nested IF() soup — use CASE.

On the example next to this theory: IF(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

IF(marks >= 40, 'Pass', 'Fail') or CASE WHEN …

IF() — sample query

-- IF()
CREATE TABLE demo (
  id INTEGER PRIMARY KEY,
  label TEXT NOT NULL,
  qty INTEGER DEFAULT 0
);
INSERT INTO demo (id, label, qty) VALUES
  (1, 'alpha', 2),
  (2, 'beta', 5);
SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

IF(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Short notes

DefIF(cond, yes, no) per row. Procedural IF is inside procedures.
RulePrefer CASE for more than two branches.
TrapMixing the two IFs.

-- IF() CREATE TABLE demo ( id INTEGER PRIMARY KEY, label TEXT NOT NULL, qty INTEGER DEFAULT 0 ); INSERT INTO demo (id, label, qty) VALUES (1, 'alpha', 2), (2, 'beta', 5); SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

IF()

IF() — sample query

Short notes

Questions

IF()

IF() — sample query

Short notes

Questions