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What is SQL?
SQL is a well know and widely accepted database language. It was first developed at IBM in the
mid 1970’s and was known as SEQUEL 2.
SQL has been accepted as an ANSI standard which strictly defines the syntax and behaviour of the
language. Needless to say there are countless variations on the standard.
Scope of the language
AQL Data Manipulation Language
As the name suggests SQL includes syntax for executing queries. We can ask questions of the
database and have the results returned in tabular form.
In addition to extracting data from a database we can insert new records, delete records and update
existing records. The query and update commands together to form the data manipulation language
(DML) component of SQL.
The four DML statements in SQL are: SELECT, UPDATE, DELETE, and INSERT.
SQL Data Definition language The data definition language (DDL) permits empty tables to be
created. We can also define keys, specify links between tables and idmpose constraints which must
always be satisfied.
The main DDL statements in SQL are: CREATE TABLE, ALTER TABLE, DROP TABLE;
CREATE INDEX and DROP INDEX.
Questions:
1) When was SQL developed?
2) What is SQL?
3) What does DML stand for?
4) How many DML statements are there?
5) What is the DDL for?
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