WHERE:

If we want to pick out a certain record or a record with a certain attribute the SQL comes with a method to do so, by using the keyword WHERE.

This will be our table 'person':

|--------------------+--------------------+--------------------|

|Name                |Age                 |Gender              |

|____________________+____________________+____________________|

|Bob                  34                   Male                |

|Silvia               67                   Female              |

|Magnus               24                   Male                |

|Lisa                 32                   Female              |

+--------------------------------------------------------------+

Syntax:

SELECT column
FROM table_name
WHERE condition

The condition we'll start by searching for all male records.

SELECT * 

FROM person 

WHERE Gender='Male';

|--------------------+--------------------+--------------------|

|Name                |Age                 |Gender              |

|____________________+____________________+____________________|

|Bob                  34                   Male                |

|Magnus               24                   Male                |

+--------------------------------------------------------------+

Now we have picked out only those records with persons having a male gender. You can use the keywords AND and OR as well.

SELECT * 

FROM person 

WHERE Gender='Male' 

AND Age<30;

|--------------------+--------------------+--------------------|

|Name                |Age                 |Gender              |

|____________________+____________________+____________________|

|Magnus               24                   Male                |

+--------------------------------------------------------------+

We can use both statements at the same time. AND will however go before OR, such as this:
('statement' AND 'statement') OR 'statement'

Just as in math, we can show what will be handled first. The AND statements can be shown above within paranthesis to illustrate how they are handled before the OR statement.

Syntax:

SELECT column
FROM table_name
WHERE condition
AND condition
OR condition

Example:

SELECT * 

FROM person

WHERE Gender='Male'

AND Age<30

OR Gender='Female'

|--------------------+--------------------+--------------------|

|Name                |Age                 |Gender              |

|____________________+____________________+____________________|

|Silvia               67                   Female              |

|Magnus               24                   Male                |

|Lisa                 32                   Female              |

+--------------------------------------------------------------+

As we can see here, we want either all records that contain a Male person under 30 years of age, or is a female. If you are female, there are no other conditions to be met. We could add more conditions if we want to, but this example is getting quite long now.

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