SQL (pronounced “ess-que-el”) stands for Structured Query Language. SQL is used to communicate with a database. According to ANSI (American National Standards Institute), it is the standard language for relational database management systems. SQL statements are used to perform tasks such as update data on a database or retrieve data from a database. Some common relational database management systems that use SQL are Oracle, Sybase, Microsoft SQL Server, Access, Ingres, etc. Although most database systems use SQL, most of them also have their own additional proprietary extensions that are usually only used on their system. However, the standard SQL commands such as “Select”, “Insert”, “Update”, “Delete”, “Create”, and “Drop” can be used to accomplish almost everything that one needs to do with a database.
| Keyword | Description |
|---|---|
| ADD | Adds a column in an existing table |
| ADD CONSTRAINT | Adds a constraint after a table is already created |
| ALTER | Adds, deletes, or modifies columns in a table, or changes the data type of a column in a table |
| ALTER COLUMN | Changes the data type of a column in a table |
| ALTER TABLE | Adds, deletes, or modifies columns in a table |
| ALL | Returns true if all of the subquery values meet the condition |
| AND | Only includes rows where both conditions is true |
| ANY | Returns true if any of the subquery values meet the condition |
| AS | Renames a column or table with an alias |
| ASC | Sorts the result set in ascending order |
| BACKUP DATABASE | Creates a back up of an existing database |
| BETWEEN | Selects values within a given range |
| CASE | Creates different outputs based on conditions |
| CHECK | A constraint that limits the value that can be placed in a column |
| COLUMN | Changes the data type of a column or deletes a column in a table |
| CONSTRAINT | Adds or deletes a constraint |
| CREATE | Creates a database, index, view, table, or procedure |
| CREATE DATABASE | Creates a new SQL database |
| CREATE INDEX | Creates an index on a table (allows duplicate values) |
| CREATE OR REPLACE VIEW | Updates a view |
| CREATE TABLE | Creates a new table in the database |
| CREATE PROCEDURE | Creates a stored procedure |
| CREATE UNIQUE INDEX | Creates a unique index on a table (no duplicate values) |
| CREATE VIEW | Creates a view based on the result set of a SELECT statement |
| DATABASE | Creates or deletes an SQL database |
| DEFAULT | A constraint that provides a default value for a column |
| DELETE | Deletes rows from a table |
| DESC | Sorts the result set in descending order |
| DISTINCT | Selects only distinct (different) values |
| DROP | Deletes a column, constraint, database, index, table, or view |
| DROP COLUMN | Deletes a column in a table |
| DROP CONSTRAINT | Deletes a UNIQUE, PRIMARY KEY, FOREIGN KEY, or CHECK constraint |
| DROP DATABASE | Deletes an existing SQL database |
| DROP DEFAULT | Deletes a DEFAULT constraint |
| DROP INDEX | Deletes an index in a table |
| DROP TABLE | Deletes an existing table in the database |
| DROP VIEW | Deletes a view |
| EXEC | Executes a stored procedure |
| EXISTS | Tests for the existence of any record in a subquery |
| FOREIGN KEY | A constraint that is a key used to link two tables together |
| FROM | Specifies which table to select or delete data from |
| FULL OUTER JOIN | Returns all rows when there is a match in either left table or right table |
| GROUP BY | Groups the result set (used with aggregate functions: COUNT, MAX, MIN, SUM, AVG) |
| HAVING | Used instead of WHERE with aggregate functions |
| IN | Allows you to specify multiple values in a WHERE clause |
| INDEX | Creates or deletes an index in a table |
| INNER JOIN | Returns rows that have matching values in both tables |
| INSERT INTO | Inserts new rows in a table |
| INSERT INTO SELECT | Copies data from one table into another table |
| IS NULL | Tests for empty values |
| IS NOT NULL | Tests for non-empty values |
| JOIN | Joins tables |
| LEFT JOIN | Returns all rows from the left table, and the matching rows from the right table |
| LIKE | Searches for a specified pattern in a column |
| LIMIT | Specifies the number of records to return in the result set |
| NOT | Only includes rows where a condition is not true |
| NOT NULL | A constraint that enforces a column to not accept NULL values |
| OR | Includes rows where either condition is true |
| ORDER BY | Sorts the result set in ascending or descending order |
| OUTER JOIN | Returns all rows when there is a match in either left table or right table |
| PRIMARY KEY | A constraint that uniquely identifies each record in a database table |
| PROCEDURE | A stored procedure |
| RIGHT JOIN | Returns all rows from the right table, and the matching rows from the left table |
| ROWNUM | Specifies the number of records to return in the result set |
| SELECT | Selects data from a database |
| SELECT DISTINCT | Selects only distinct (different) values |
| SELECT INTO | Copies data from one table into a new table |
| SELECT TOP | Specifies the number of records to return in the result set |
| SET | Specifies which columns and values that should be updated in a table |
| TABLE | Creates a table, or adds, deletes, or modifies columns in a table, or deletes a table or data inside a table |
| TOP | Specifies the number of records to return in the result set |
| TRUNCATE TABLE | Deletes the data inside a table, but not the table itself |
| UNION | Combines the result set of two or more SELECT statements (only distinct values) |
| UNION ALL | Combines the result set of two or more SELECT statements (allows duplicate values) |
| UNIQUE | A constraint that ensures that all values in a column are unique |
| UPDATE | Updates existing rows in a table |
| VALUES | Specifies the values of an INSERT INTO statement |
| VIEW | Creates, updates, or deletes a view |
| WHERE | Filters a result set to include only records that fulfill a specified condition |
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