Insert (SQL)
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An SQL INSERT statement adds one or more records to a table in a relational database. An INSERT statement can only insert data into a single table.
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[edit] Basic form
Insert statements have the following form:
- INSERT INTO table (column1, [column2, ... ]) VALUES (value1, [value2, ...])
The number of columns and values must be the same. If a column is not specified, the default value for the column is used. The values specified (or implied) by the INSERT statement must satisfy all the applicable constraints (such as primary keys, CHECK constraints, and NOT NULL constraints). If a syntax error occurs or if any constraints are violated, the new row is not added to the table and an error returned instead.
Example:
INSERT INTO phone_book (name, number) VALUES ('John Doe', '555-1212');
When values for all columns in the table are specified, then a shorthand may be used, taking advantage of the order of the columns when the table was created:
- INSERT INTO table VALUES (value1, [value2, ...])
Example (assuming that 'name' and 'number' are the only columns in the 'phone_book' table):
INSERT INTO phone_book VALUES ('John Doe', '555-1212');
[edit] Advanced forms
[edit] Multirow inserts
An SQL feature (since SQL-92) is the use of row value constructors to insert multiple rows at a time in a single SQL statement:
INSERT INTO table (column1, [column2, ... ]) VALUES (value1a, [value1b, ...]), (value2a, [value2b, ...]), ...
This feature is supported by DB2, PostgreSQL and MySQL.
Example (assuming that 'name' and 'number' are the only columns in the 'phone_book' table):
INSERT INTO phone_book VALUES ('John Doe', '555-1212'), ('Peter Doe', '555-2323');
which may be seen as a shorthand for the two statements
INSERT INTO phone_book VALUES ('John Doe', '555-1212');
INSERT INTO phone_book VALUES ('Peter Doe', '555-2323');
Note that the two separate statements may have different semantics (especially with respect to statement triggers) and may not provide the same performance as a single multi-row insert.
To insert multiple rows in MS SQL you can use such a construction:
INSERT INTO phone_book SELECT 'Prakash Patel', '555-1212' UNION ALL SELECT 'Peter Doe', '555-2323';
Note that this is not a valid SQL statement according to the SQL standard (SQL:2003) due to the incomplete subselect clause.
To do the same in Oracle use the DUAL table, which always consists of a single row only:
INSERT INTO phone_book SELECT 'Prakash Patel', '555-1212' FROM DUAL UNION ALL SELECT 'Peter Doe','555-2323' FROM DUAL
A standard-conforming implementation of this logic shows the following example, or as shown above:
INSERT INTO phone_book SELECT 'Prakash Patel', '555-1212' FROM LATERAL ( VALUES (1) ) AS t(c) UNION ALL SELECT 'Peter Doe','555-2323' FROM LATERAL ( VALUES (1) ) AS t(c)
[edit] Copying rows from other tables
An INSERT statement can also be used to retrieve data from other, modify it if necessary and insert it directly into the table. All this is done in a single SQL statement that does not involve any intermediary processing in the client application. A subselect is used instead of the VALUES clause. The subselect can contain joins, function calls, and it can even query the same table into which the data is inserted. Logically, the select is evaluated before the actual insert operation is started. An example is given below.
INSERT INTO phone_book2
SELECT *
FROM phone_book
WHERE name IN ('John Doe', 'Peter Doe')
The SELECT statement produces a (temporary) table, and the schema of that temporary table must match with the schema of the table where the data is inserted into.
[edit] Retrieving the key
Database designers that use a surrogate key as the primary key for every table will run into the occasional scenario where they need to automatically retrieve the database generated primary key from a SQL INSERT statement for use in another SQL statements. Most systems do not allow SQL INSERT statements to return row data. Therefore, it becomes necessary to implement a workaround in such scenarios. Common implementations include:
- Using a database-specific stored procedure that generates the surrogate key, performs the INSERT operation, and finally returns the generated key.
- Using a database-specific SELECT statement on a temporary table containing last inserted row(s). DB2 implements this feature in the following way:
SELECT * FROM NEW TABLE ( INSERT INTO phone_book VALUES ( 'Peter Doe','555-2323' ) ) AS t
- Using a SELECT statement after the INSERT statement with a database-specific function that returns the generated primary key for the most recently inserted row.
- Using a unique combination of elements from the original SQL INSERT in a subsequent SELECT statement.
- Using a GUID in the SQL INSERT statement and retrieving it in a SELECT statement.
[edit] Triggers
If triggers are defined on the table on which the INSERT statement operates, those triggers are evaluated in the context of the operation. BEFORE INSERT triggers allow the modification of the values that shall be inserted into the table. AFTER INSERT triggers cannot modify the data anymore, but can be used to initiate actions on other tables, for example to implement auditing mechanisms.
