Select Dataselect statement is used to query data from a database. A select statement
might be as follows:
select user, pass, page from members
where user = 'John';
"user", "pass" and "page" are column names.
You can select as many column names as you want, or you can use a "*" to select
all columns:
select * from members
where user = 'John';
"members" is table name that follows the keyword from.
The where clause (optional) specifies which data values or rows will
be returned or displayed, based on the criteria described after the keyword
where. Note: if the value is a string, then it should be enclosed in
single quotes, and numbers should not.
You can use any of the following logical operators in your where
clause to restrict the rows you retrieve.
| Logical Operators |
| = |
Equal to |
| != or <> |
Not equal to |
| > |
Greater than |
| >= |
Greater than or equal to |
| < |
Less than |
| <= |
Less than or equal to |
| in |
Equal to any item in a list |
| not in |
Not equal to any item in a list |
| between |
Between two values,
greater than or equal to one and less than or equal to the other |
| not between |
Not between two values |
| begins with |
Begins with specified value |
| contains |
Contains specified value |
| not contains |
Does not contain specified value |
| is null |
Is blank |
| is not null |
Is not blank |
| like |
Like a specified pattern.
% means any series of characters.
_ means any single character. |
| not like |
Not like a specified pattern.
% means any series of characters.
_ means many single character. |
like allows you to select all data that is similar to what you specify.
In SQL, the percent symbol "%" acts as a wildcard to represent any
string of characters, including an empty string, and the underscore character
"_" acts as a wildcard to represent any single character. For example:
select user, pass, page from members
where user LIKE 'Jo%';
This statement will match any user names that start with 'Jo'.
Or you can specify,
select user, pass, page from members
where user LIKE '%e';
This statement will match any last names that end in a 'e'.
Examples of some other operators:
select price from product where price > 10;
select * from product where price between 10 and 100;
You can use key words order by for sorting your data. For example, you
can order your data by user name.
select * from members
order by user
By default, order by clause orders the specified fields in ascending
order.
If you want the data in the specified field displayed in descending order
(Z to A, 100 to 1), you can add "desc" after a column name:
select * from members
order by user desc
You can add multiple criteria to your where clauses by using "and" or
"or.":
select user, pass, page from members
where user = 'John' and pass='John123';
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