sql.md

SQL

SELECT statement

Used to retrieve records from a database.

Syntax

SELECT column1, column2, ...
  FROM table_name;

SELECT *
  FROM table_name;

Examples

Retrieve all records, showing column1 and column2, from the table_name table:

SELECT column1, column2
  FROM table_name;

Retrieve all records, showing all columns, from the table_name table:

SELECT *
  FROM table_name;

SELECT DISTINCT statement

Used to return unique values.

Syntax

SELECT DISTINCT column1, column2, ...
           FROM table_name;

Examples

Retrieve all (unique) records, showing column1 and column2, from the table_name table:

SELECT DISTINCT column1, column2
           FROM table_name;

Retrieve the total number of unique column1 values, from the table_name table:

SELECT COUNT(DISTINCT column1)
        FROM table_name;

WHERE clause

Used to filter records via a specified condition.

Operators in the WHERE clause:

Operator	Description
=	Equal
<> or !=	Not equal
>	Greater than
<	Less than
>=	Greater than or equal
<=	Less than or equal
BETWEEN	Between a certain range
LIKE	Search for a pattern
IN	To specify multiple possible values for a column

Syntax

SELECT column1, column2, ...
  FROM table_name
 WHERE condition;

Note: Also used in UPDATE and DELETE statements.

Examples

Retrieve records (showing all columns), from the table_name, table where column1 is foo:

SELECT *
  FROM table_name
 WHERE column1 = 'foo';

Retrieve records (showing all columns), from the table_name, table where column1 is 1:

SELECT *
  FROM table_name
 WHERE column1 = 1;

AND, OR and NOT operators

Used in combination with WHERE to further filter records.

Syntax

AND

SELECT column1, column2, ...
  FROM table_name
 WHERE condition1
   AND condition2
   AND condition3 ...;

OR

SELECT column1, column2, ...
  FROM table_name
 WHERE condition1
    OR condition2
    OR condition3 ...;

NOT

    SELECT column1, column2, ...
      FROM table_name
 WHERE NOT condition;

Examples

Retrieve records (showing all columns), from the table_name table, where column1 is foo and column2 is bar:

SELECT *
  FROM table_name
 WHERE column1 = 'foo'
   AND column2 = 'bar';

Retrieve records (showing all columns), from the table_name table, where column1 is foo or bar:

SELECT *
  FROM table_name
 WHERE column1 = 'foo'
    OR column1 = 'bar';

Retrieve records (showing all columns), from the table_name table, where column1 is not foo:

    SELECT *
      FROM table_name
 WHERE NOT column1 = 'foo';

ORDER BY keyword

Used to sort the result set in ascending or descending order.

Syntax

  SELECT column1, column2, ...
    FROM table_name
ORDER BY column1, column2, ... ASC|DESC;

Examples

Retrieve all records (showing all columns), from the table_name table, sorted ascending by the column1 column:

  SELECT *
    FROM table_name
ORDER BY column1 ASC;

Retrieve all records (showing all columns), from the table_name table, sorted descending by the column1 column:

  SELECT *
    FROM table_name
ORDER BY column1 DESC;

Retrieve all records (showing all columns), from the table_name table, sorted by the column1 column, if some records have the same column1 value then sort by column2:

  SELECT *
    FROM table_name
ORDER BY column1, column2;

INSERT INTO statement

Syntax

INSERT INTO table_name
            (column1, column2, column3, ...)
     VALUES (value1, value2, value3, ...);

When inserting values for all columns specifiying the column names is unnecessary:

INSERT INTO table_name
     VALUES (value1, value2, value3, ...);

Examples

Insert a new record with values as follows: column1=foo, column2=bar, column3=foobar:

INSERT INTO table_name
            (column1, column2, column3)
     VALUES ('foo', 'bar', 'foobar');

NULL Values

The representation of the absence of a value. Different than 0, empty string or .

Syntax

IS NULL

SELECT column1
  FROM table_name
 WHERE column1 IS NULL;

IS NOT NULL

SELECT column1
  FROM table_name
 WHERE column1 IS NOT NULL;

Examples

Retrieve records (showing column column1), from the table_name table, where column1 value is NULL:

SELECT column1
  FROM table_name
 WHERE column1 IS NULL;

Retrieve records (showing column column1), from the table_name table, where column1 value is not NULL:

SELECT column1
  FROM table_name
 WHERE column1 IS NOT NULL;

UPDATE statement

Used to modify existing records in a table.

Syntax

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

Note: Remember to include a WHERE clause.

Examples

Update column2 field with foo and column3 field with bar, for the record that has a value of 1 on column1 field, on the table_name table:

UPDATE table_name
   SET column2 = 'foo',
       column3 = 'bar'
 WHERE column1 = 1;

Update column1 field with foo, for all records, on the table_name table:

UPDATE table_name
   SET column1 = 'foo';

DELETE statement

Used to delete records in a table.

Syntax

DELETE FROM table_name
      WHERE condition;

Note: Remember to include a WHERE clause.

Examples

Delete the records, on table table_name, that have the value foo on the column1 field:

DELETE FROM table_name
      WHERE column1 = 'foo';

Delete all records on the table table_name:

DELETE FROM table_name;