4. SQL Statements : UPDATE
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Valid in: SQL, ESQL, OpenAPI, ODBC, JDBC, .NET
The UPDATE statement updates column values in a table.
This statement has the following formats:
Interactive version:
UPDATE [schema.]table_name [corr_name]
              [FROM [schema.]table_name [corr_name]
              { , [schema.]table_name [corr_name]}]
              SET column_name = expression {, column_name = expression}
              [WHERE search_condition];
Embedded non-cursor version:
EXEC SQL [REPEATED] UPDATE [schema.]table_name [corr_name]
              [FROM [schema.]table_name [corr_name]
              { , [schema.]table_name [corr_name]}]
              SET column = expression {, column = expression}
              [WHERE search_condition];
The UPDATE statement replaces the values of the specified columns by the values of the specified expressions for all rows of the table that satisfy the search_condition.
If a row update violates an integrity constraint on the table, the update is not performed. table_name specifies the table for which the constraint is defined. A correlation name (corr_name) can be specified for the table for use in the search_condition. For a definition of correlation names and discussion of their use, see the chapter “Introducing SQL.”
The expressions in the SET clause can use constants or column values from the table being updated or from any tables listed in the FROM clause. They also can be a scalar subquery (a SELECT statement that returns 0 or 1 rows and has a single entry in the select list).
If a column name specifies a numeric column, its associated expression must evaluate to a numeric value. Similarly, if a column name represents a character type, its associated expression must evaluate to a character type.
The result of a correlated aggregate cannot be assigned to a column. For example, the following UPDATE statement is invalid:
UPDATE mytable FROM yourtable
      SET mytable.mycolumn = MAX(yourtable.yourcolumn);
To assign a null to a nullable column, use the null constant.