Expressions Conditions And Operators

Expressions

An expression returns a value.

Conditions

If you ever want to find a particular item or group of items in your database, you need
one or more conditions. Conditions are contained in the WHERE clause.

The WHERE clause

The syntax of the WHERE clause is

WHERE <SEARCH CONDITION>

Operators

Operators are the elements you use inside an expression to articulate how you want
specified conditions to retrieve data.

Arithmetic Operators

The arithmetic operators are plus (+), minus (-), divide (/), multiply (*), and modulo (%).

Comparison Operators

True to their name, comparison operators compare expressions and return one of three
values: TRUE, FALSE, or Unknown.

In database terms NULL is the absence of data in a field.

Character Operators

You can use character operators to manipulate the way character strings are
represented, both in the output of data and in the process of placing conditions on data
to be retrieved.

Logical Operators

Logical operators separate two or more conditions in the WHERE clause.

Set Operators

Miscellaneous Operators: IN and BETWEEN

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