SQL · Theory

From_days()

Theory

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From_days()

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

Pattern: USE college; then a CREATE/SELECT/UPDATE that needs From_days(). 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 From_days() 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: From_days(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Diagram

  FROM students
        │
        ▼
  WHERE city = 'Pune'
        │
        ▼
  SELECT name, marks

Exam tip

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

From_days() — sample query

-- From_days()
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;

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

Short notes

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

SQL · Theory

From_days()

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Theory

226/439

From_days()

Pattern: USE college; then a CREATE/SELECT/UPDATE that needs From_days(). 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: From_days(): create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Diagram

  FROM students
        │
        ▼
  WHERE city = 'Pune'
        │
        ▼
  SELECT name, marks

Exam tip

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

From_days() — sample query

-- From_days()
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;

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

Short notes

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

From_days()

From_days() — sample query

Short notes

Questions

From_days()

From_days() — sample query

Short notes

Questions