#mysql query

MySQL UPDATE Statement

The UPDATE statement is used to modify the existing records in a table.

UPDATE Syntax:

UPDATE table_name SET column1 = value1, column2 = value2, … WHERE condition;

Be careful when updating records in a table! Notice the WHERE clause in the UPDATE statement. The WHERE clause specifies which record(s) that should be updated. If you omit the WHERE clause, all records in the…

MySQL where condition

  WHERE Syntax SELECT column1, column2, … FROM table_name WHERE condition;

Note: The WHERE clause is not only used in SELECT statement, it is also used in UPDATE, DELETE statement, etc.!

SELECT * FROM Customers WHERE Country=’Mexico’;

  Operators in The WHERE Clause

The following operators can be used in the WHERE clause:

Operator Description = Equal <> Not equal. 

mysql – sql query to fetch count of employee

mysql – sql query to fetch count of employee

  mysql – sql query to fetch count of employee

How MySQL Optimizes WHERE Clauses

Some of the optimizations performed by MySQL on where clauses as follow: Removal of unnecessary parentheses: ((a AND b) AND c OR (((a AND b) AND (c AND d)))) To (a AND b AND c) OR (a AND b AND c AND d) Constant folding: (a5 AND b=c AND a=5 Constant condition removal (needed because of constant folding): (B>=5 AND B=5) OR (B=6 AND 5=5) OR (B=7 AND 5=6) To B=5 OR B=6 Constant expressions used…