Selecting Data

Relational Databases

Selecting Data

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Let's see how we can begin to select data from tables through code!

The select statement is used to query the database and retrieve data that matches what you're looking for and specify within your code!

The format can be shown below:

Enter this query into this link from W3 Schools and see the result!

SELECT * FROM Customers;

You can select as many columns as you would like, or you can use a * to select all columns!

As you can see the resulting query shows the number of records is equal to 91 and shows all of the records of customers in the database.

The WHERE Clause

Conditional selections used in the where clause are:

  • = equal
  • > greater
  • < less than
  • >= Greater than or equal
  • <= Less than or equal
  • <> Not equal to

In the web3 Schools try copying the following query and see the result.

SELECT * FROM Customers
WHERE CustomerID = 1;

Try playing witht he WHERE clause and see the different results you get!!

The LIKE Conditional Selection

The LIKE pattern matching operator can also be used in the conditional selection of the where clause. Like is a very powerful operator that allows you to select only rows that are similar to what you specify.

The percent sign % can be used as a wild card variable to match any possible character that might appear before or after the characters specified. For example:

SELECT * FROM Customers
WHERE CustomerName LIKE 'A%';

This will match and select any matches of customer names that start with A

But remember… Strings must be in single quotes!

Specifying Exact Data Queries

We can also specify exact data we are looking to select.

The * to select all records of a function.

Easy enough? Perfect, Let's move on!

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