SQL · Theory

STRCMP()()

Theory

168/439

STRCMP()()

STRCMP() compare two strings: 0 equal, -1 / 1 order. You use it in SELECT (and sometimes WHERE/UPDATE). It does not change stored data unless you UPDATE … SET col = STRCMP(col).

Board: SELECT STRCMP('Asha','Kabir'); Run it. Say the result out loud. If the column is NULL, the result is often NULL — wrap with IFNULL if you need a blank instead.

String indexes in MySQL start at 1, not 0 (SUBSTR, INSTR, LEFT). Depends on collation.

Interview — name STRCMP, one argument list, one example on the students table. Don’t recite every string function.

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

Exam tip

Say what STRCMP returns, then SELECT STRCMP('Asha','Kabir');

STRCMP()() — sample query

-- STRCMP()()
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;

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

Short notes

DefSTRCMP() compare two strings: 0 equal, -1 / 1 order.
RuleSELECT STRCMP('Asha','Kabir');
TrapDepends on collation.

SQL · Theory

STRCMP()()

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Theory

168/439

STRCMP()()

STRCMP() compare two strings: 0 equal, -1 / 1 order. You use it in SELECT (and sometimes WHERE/UPDATE). It does not change stored data unless you UPDATE … SET col = STRCMP(col).

Board: SELECT STRCMP('Asha','Kabir'); Run it. Say the result out loud. If the column is NULL, the result is often NULL — wrap with IFNULL if you need a blank instead.

String indexes in MySQL start at 1, not 0 (SUBSTR, INSTR, LEFT). Depends on collation.

Interview — name STRCMP, one argument list, one example on the students table. Don’t recite every string function.

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

Exam tip

Say what STRCMP returns, then SELECT STRCMP('Asha','Kabir');

STRCMP()() — sample query

-- STRCMP()()
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;

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

Short notes

DefSTRCMP() compare two strings: 0 equal, -1 / 1 order.
RuleSELECT STRCMP('Asha','Kabir');
TrapDepends on collation.

STRCMP()()

STRCMP()() — sample query

Short notes

Questions

STRCMP()()

STRCMP()() — sample query

Short notes

Questions