DML (Data Manipulation Language). These SQL statements are used to retrieve and manipulate data. This category encompasses the most fundamental commands including DELETE, INSERT, SELECT, and UPDATE. DML SQL statements have only minor differences between SQL variations.
Conceptually a relational database provides these functions for accessing data:
- Select. Show records of a table that have specified values in specified fields.
- Project. Show specified fields of a table.
- Join. Show more than one table as if it were one table.
The results of a query are often individual values, sequences of values, or some times a recordset (aka CURSOR (CURrent Set Of Records)) which may be a sub set from one or more tables.
Most data manipulation operations are performed by these four fundamental DML SQL commands:
- DELETE to remove rows.
- INSERT to add a row.
- SELECT to retrieve row.
- UPDATE to change data in specified columns.
There are three SQL clauses that deserve their own page:
- FROM specifies the table or view sources used by its command.
- JOIN logically relates multiple table or view sources so as to retrieve a single result set.
- WHERE specifies the rows used by its command.
- GROUP BY takes the results of a SELECT command, divides it into groups, and produces a result set with one row per group.
There are other SQL DML statements:
- UNION appends a result set to another result set with similar structure.
- COMPUTE tacks on a 1 row result set with aggregate information about its parent result set.