SQL Basic Syntax

SQL SELECT Statement

Select statements are used to select data from a table.

The result is stored in a result table, called a result set.

SQL SELECT Syntax

SELECT column name from table name

And:

SELECT * FROM table name

Note: The SQL statement is not case sensitive. Select is equivalent to select.

To get the contents of a column named "LastName" and "FirstName" (from a database table named "Persons"), use a SELECT statement like this:

SELECT Lastname,firstname from Persons

*From Persons

Tip: An asterisk (*) is a shortcut to select all columns.

SQL SELECT DISTINCT Statement

In the table, duplicate values may be included. That's not a problem, but sometimes you might want to just list different values (distinct).

Keyword DISTINCT is used to return only different values.

Grammar:

SELECT DISTINCT column name from table name

The WHERE clause is used to specify the criteria for selection.

WHERE clause

To conditionally select data from a table, you can add a WHERE clause to the SELECT statement.

Grammar

SELECT column name from table name WHERE column operator value

If you want to select only people who live in the city "Beijing", we need to add a WHERE clause to the SELECT statement:

WHERE City=‘Beijing‘

Use of quotation marks

Note that we use single quotes around the condition values in the example.

SQL uses single quotation marks to wrap text values (most database systems also accept double quotes). If it is a numeric value , do not use quotation marks.

And and OR operators

And and or can combine two or more conditions in a where sub-statement.

If both the first condition and the second condition are true, the AND operator displays a record.

If only one of the first and second conditions is true, the OR operator displays a record.

ANDLastname= ' Carter '

Combine and and OR operators

We can also combine and and or together (using parentheses to form complex expressions):

(ORFirstname= ' William ' ) AND lastname= ' Carter '

ORDER by statement

The order BY statement is used to sort the result set based on the specified column.

The order BY statement sorts records by default in ascending order.

If you want to sort records in descending order, you can use the DESC keyword.

Show company name in alphabetical order:

ORDER BY Company

Show company name in reverse alphabetical order:

ORDER BY Company DESC

INSERT into statement

The INSERT INTO statement is used to insert a new row into the table.

Grammar

INSERT into table name values (value 1, value 2,....)

We can also specify the columns for which you want to insert data:

INSERT into table_name (column 1, column 2,...) Values (value 1, value 2,....)

Update statement

The Update statement is used to modify the data in the table.

Grammar:

UPDATE table name SET column name = new value WHERE Column name = value

To update a column in a row

We add FirstName for LastName who is "Wilson":

To update several columns in a row

We will modify the address and add the city name:

UPDATE person SET Address = ' Zhongshan ", city = ' nanjing ' WHERE LastName = ' Wilson '

DELETE statement

The DELETE statement is used to delete rows in a table.

Grammar

DELETE from table name WHERE column name = value

Delete a row

"Fred Wilson" will be removed:

Delete all rows

You can delete all rows without deleting the table. This means that the structure, properties, and indexes of the table are complete:

DELETE from table_name

Or:

DELETE * FROM table_name

SQL Basic Syntax