SQL · Theory

period_add()

Theory

242/439

period_add()

period_add() is a MySQL topic you learn with one small college example — a students table with roll, name, marks. Say what period_add() does in one sentence, then write the shortest SQL that shows it.

Pattern: USE college; then a CREATE/SELECT/UPDATE that needs period_add(). If it is a function, SELECT it on one column. If it is DDL, run SHOW / DESCRIBE after so you can see the change.

Trap: only reciting the heading period_add() with no SQL. Interviewers ask you to type. Another trap: mixing this up with a neighbouring command (DELETE vs TRUNCATE vs DROP, WHERE vs HAVING, JOIN vs UNION).

Keep the example on paper — two or three rows. Change one value. Predict the result before you run it.

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

Exam tip

What is period_add()? One sentence + one tiny SQL on students.

period_add() — sample query

-- period_add()
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;

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

Short notes

Defperiod_add() — explain with students(roll, name, marks).
RuleShortest SQL that uses period_add(). Then SHOW/SELECT the effect.
TrapHeading only, no query. Mixing nearby commands.

SQL · Theory

period_add()

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Theory

242/439

period_add()

Pattern: USE college; then a CREATE/SELECT/UPDATE that needs period_add(). If it is a function, SELECT it on one column. If it is DDL, run SHOW / DESCRIBE after so you can see the change.

Keep the example on paper — two or three rows. Change one value. Predict the result before you run it.

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

Exam tip

What is period_add()? One sentence + one tiny SQL on students.

period_add() — sample query

-- period_add()
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;

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

Short notes

Defperiod_add() — explain with students(roll, name, marks).
RuleShortest SQL that uses period_add(). Then SHOW/SELECT the effect.
TrapHeading only, no query. Mixing nearby commands.

period_add()

period_add() — sample query

Short notes

Questions

period_add()

period_add() — sample query

Short notes

Questions