SQL · Theory

Slow Query Log

Theory

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Slow Query Log

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

Pattern: USE college; then a CREATE/SELECT/UPDATE that needs Slow Query Log. 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 Slow Query Log 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 — Slow Query Log — sELECT projects columns; WHERE filters; ORDER BY sorts.

Exam tip

What is Slow Query Log? One sentence + one tiny SQL on students.

Slow Query Log — sample query

CREATE TABLE employees (id INTEGER PRIMARY KEY, name TEXT, dept TEXT, salary INTEGER);
INSERT INTO employees VALUES
  (1, 'Asha', 'Eng', 70000),
  (2, 'Ravi', 'Eng', 65000),
  (3, 'Neha', 'HR', 50000);
SELECT name, salary FROM employees WHERE dept = 'Eng' ORDER BY salary DESC;

Slow Query Log — sELECT projects columns; WHERE filters; ORDER BY sorts.

Short notes

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

SQL · Theory

Slow Query Log

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Theory

384/439

Slow Query Log

Pattern: USE college; then a CREATE/SELECT/UPDATE that needs Slow Query Log. 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 — Slow Query Log — sELECT projects columns; WHERE filters; ORDER BY sorts.

Exam tip

What is Slow Query Log? One sentence + one tiny SQL on students.

Slow Query Log — sample query

CREATE TABLE employees (id INTEGER PRIMARY KEY, name TEXT, dept TEXT, salary INTEGER);
INSERT INTO employees VALUES
  (1, 'Asha', 'Eng', 70000),
  (2, 'Ravi', 'Eng', 65000),
  (3, 'Neha', 'HR', 50000);
SELECT name, salary FROM employees WHERE dept = 'Eng' ORDER BY salary DESC;

Slow Query Log — sELECT projects columns; WHERE filters; ORDER BY sorts.

Short notes

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

Slow Query Log

Slow Query Log — sample query

Short notes

Questions

Slow Query Log

Slow Query Log — sample query

Short notes

Questions