When a row on one table is related to one or more rows in another table This is called a?

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DML Commands - General

Updates specified rows in the target table with new values.

In this Topic:

Syntax¶

UPDATE 
       SET  =  [ ,  =  , ... ]
        [ FROM  ]
        [ WHERE  ]

Required Parameters¶

Specifies the table to update.

Specifies the name of a column in target_table. Do not include the table name. For example, UPDATE t1 SET t1.col = 1 is invalid.

Specifies the new value to set in col_name.

Optional Parameters¶

Specifies one or more tables to use for selecting rows to update or for setting new values. Note that repeating the target table results in a self-join.

Expression that specifies the rows in the target table to update.

Default: No value (all rows of the target table are updated)

Usage Notes¶

• When a FROM clause contains a JOIN between tables (e.g. t1 and t2), a target row in t1 may join against (i.e. match) more than one row in table t2. When this occurs, the target row is called a multi-joined row. When updating a multi-joined row, the ERROR_ON_NONDETERMINISTIC_UPDATE session parameter controls the outcome of the update:

  • If FALSE (default value), no error is returned and one of the joined rows is used to update the target row; however, the selected joined row is nondeterministic.

  • IF TRUE, an error is returned, including an example of the values of a target row that joins multiple rows.

  To set the parameter:

  ALTER SESSION SET ERROR_ON_NONDETERMINISTIC_UPDATE=TRUE;
  

Examples¶

Perform a standard update using two tables:

UPDATE t1
  SET number_column = t1.number_column + t2.number_column, t1.text_column = 'ASDF'
  FROM t2
  WHERE t1.key_column = t2.t1_key and t1.number_column < 10;

Update with join that produces nondeterministic results:

select * from target;

+---+----+
| K |  V |
|---+----|
| 0 | 10 |
+---+----+

Select * from src;

+---+----+
| K |  V |
|---+----|
| 0 | 11 |
| 0 | 12 |
| 0 | 13 |
+---+----+

-- Following statement joins all three rows in src against the single row in target
UPDATE target
  SET v = src.v
  FROM src
  WHERE target.k = src.k;

+------------------------+-------------------------------------+
| number of rows updated | number of multi-joined rows updated |
|------------------------+-------------------------------------|
|                      1 |                                   1 |
+------------------------+-------------------------------------+

• With ERROR_ON_NONDETERMINISTIC_UPDATE = FALSE, the statement randomly updates the single row in target using values from one of the following rows in src:

  (0, 11) , (0, 12) , (0,13)

• With ERROR_ON_NONDETERMINISTIC_UPDATE = TRUE, an error is returned reporting a duplicate DML row [0, 10].

To avoid this nondeterministic behavior and error, use a 1-to-1 join:

UPDATE target SET v = b.v
  FROM (SELECT k, MIN(v) v FROM src GROUP BY k) b
  WHERE target.k = b.k;

This statement results in the single row in target updated to (0, 11) (values from the row with the minimum value for v in src) and will never result in an error.

When a row in one table can be associated with one or more rows in another table and vice versa This is called a?

What is a one

What is it called when one record from a table can be associated with only one record from another table?

What is a link between two tables called?