SQL · Theory

GROUP_CONCAT()

Theory

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GROUP_CONCAT()

GROUP_CONCAT() is simple if you keep it on paper. Meera uses it for GROUP_CONCAT on Meera's board in a first job task.

Do GROUP_CONCAT() once by hand. one GROUP_CONCAT step Meera can write from memory. Change one input. Say the new result out loud.

Skip GROUP_CONCAT() and copy-pasting GROUP_CONCAT without a dry-run shows up in a first job task.

Meera ships GROUP_CONCAT() in a first job task. That is the use case worth saying.

Don’t do this with GROUP_CONCAT() — copy-pasting GROUP_CONCAT without a dry-run. Interviewers spot it in ten seconds.

Place GROUP_CONCAT() next to nearby SQL work — one GROUP_CONCAT step Meera can write from memory is the link.

Viva for GROUP_CONCAT(): what it is → one GROUP_CONCAT step Meera can write from memory → the mistake (copy-pasting GROUP_CONCAT without a dry-run).

Exam tip

Say GROUP_CONCAT() in one breath, then one GROUP_CONCAT step Meera can write from memory, then copy-pasting GROUP_CONCAT without a dry-run.

GROUP_CONCAT() — sample query

-- GROUP_CONCAT()
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;

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

Short notes

DefGROUP_CONCAT() — Meera uses it for GROUP_CONCAT on Meera's board in a first job task.
RuleGROUP_CONCAT() → one GROUP_CONCAT step Meera can write from memory.
RememberGROUP_CONCAT() + an index (a first job task).
UseGROUP_CONCAT() in a first job task (GROUP_CONCAT on Meera's board).
TrapGROUP_CONCAT() — copy-pasting GROUP_CONCAT without a dry-run.
ExGROUP_CONCAT() → GROUP_CONCAT on Meera's board.

-- GROUP_CONCAT() 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;

GROUP_CONCAT()

GROUP_CONCAT() — sample query

Short notes

Questions

GROUP_CONCAT()

GROUP_CONCAT() — sample query

Short notes

Questions