لغة الاستعلام

identifies the columns to be displayed

• SELECT

• FROM

• WHERE

identifies the table containing those columns

• SELECT

• FROM

• WHERE

Return one result

per row

• Single-row

  functions

• Multiple-row

  functions

Return one result

per set of rows

• Single-row

  functions

• Multiple-row

  functions

is a character, a number, or a date that is included in the SELECT statement.

• Column Alias

• Concatenation Operator

• Literal Character Strings

• Null Value

is a value that is unavailable, unassigned, unknown, or inapplicable.

• Literal Character Strings

• Concatenation Operator

• Column Alias

• Null Value

Is represented by two vertical bars (||)

• Literal Character Strings

• Concatenation Operator

• Column Alias

• Null Values

is not the same as a zero or a blank space.

• Column Alias

• Concatenation Operator

• Null Values

• Literal Character Strings

Links columns or character strings to other columns

• column alias

• Concatenation Operator

• Literal Character Strings

• Null Value

Renames a column heading

• Column Alias

• Concatenation Operator

• Literal Character Strings

• Null Value