Using Date in Where Clause.Your update statementupdate table.If you are trying to compare to specific date you dont need the inner query, for example update table.DDMMYY lt date. You can adjust date format mask to whatever format of data you prefer.SQL is a standardized query language that is supported by all compliant relational databases with some proprietary extensions sometimes.Summary+A+multiple-column+subquery+returns+more+than+one+column..jpg' alt='Oracle Subselect In Update Statement Oracle' title='Oracle Subselect In Update Statement Oracle' />Unfortunately, the answer is no.DB2 did not transform the UPDATE statement with a noncorrelated subselect to a join because multiple values can qualify in the inner.PostgreSQL, often simply Postgres, is an objectrelational database management system ORDBMS with an emphasis on extensibility and standards compliance.Based+on+Introduction+to+Oracle%3A+SQL+and+PL%2FSQL.jpg' alt='Oracle Subselect In Update Statement Oracle' title='Oracle Subselect In Update Statement Oracle' />SQL is not a programming language.PLSQL is a procedural programming language that is supported on Oracle only Postgres has similar syntax.PLSQL is SQL regular programming language features like conditional statements ifelse, loops for, functions and procedures and such.PLSQL is used whenever its too difficult or impossible to get some data using SQL solely.UPDATE and DELETE with Subselects IBM DB2 Wiki IBM DB2.One might ask if a subselect like that shown here can be rewritten as a join so that an index can be used on SPJ.SN. Click here to see the sample tables referenced in this topic.UPDATE SPJ. WHERE STATUS 1.Unfortunately, the answer is no.DB2 did not transform the UPDATE statement with a non correlated subselect to a join because multiple values can qualify in the inner select.However, the statement can be rewritten as a correlated subselect which can be transformed to a join as follows and a matching index scan used on SPJX.SN with index only processing and a matching index scan can be used on SX.SN. However, a sort is required on the qualifying rows in the SPJ table for the join and to get unique values.UPDATE SPJ SPJX. FROM S SX.WHERE SPJX. SN SX.SN. AND STATUS 1.If many rows qualify and must be sorted and the statement cannot be rewritten as a correlated statement, an alternative is to separate the update into component parts in this case, a cursor select and an update.For example, you can use the following pseudo code, which uses a matching index scan on SN in the SPJ table for setting QTY0 for suppliers with a STATUS of 1.DECLARE SCURSOR CURSOR FOR.WHERE STATUS 1. FETCH SCURSOR INTO SN.IF SQLCODE 1. 00.GO TO COMPLETED UPDATE.WHERE SPJ. SN SN.GO TO FETCH NEXT SN.COMPLETED UPDATE.In general, it is preferable to do as much processing as possible in a single SQL statement but there are exceptions.You can set a column equal to the result of a subselect that returns only one set of values.If more than one row qualifies in the subselect, a 8.SQLCODE is returned for a non correlated subselect V6 APAR PQ3.Below is an example of updating the SPJ.PN column to the value in P.PN for bolt if SPJ.SN contains S4. WHERE PNAME Bolt.WHERE SN S4. The following statement is an extension of the previous statement which shows that multiple columns in a table can be set to multiple columns resulting from a subselect and that an expression can be used in the subselect.SET PN, QTY. SELECT PN, QTY 1.WHERE PNAME Bolt.A GROUP BY in a statement usually results in more than one row qualifying.Therefore, it is not allowed when updating columns according to the result of a subselect a 8.SQLCODE is returned.The subselect in the SET clause can include an expression, NULL provided that the column being updated allows for nulls, or the keyword DEFAULT meaning the default established when the table was created.If no rows qualify in the subselect, null is returned.The column is assigned null if it allows for null based on nullability of column specified when the table was created.If the column does not allow for null, an error of 4. Razer Game Booster 3 5 6 0 Beta 2012 Movie . SQLCODE is received.Explanation of Update and Delete Based on Results of Inner Select The SET clause of an UPDATE statement can contain an inner select.The WHERE clause of a searched DELETE statement can contain an inner select.The inner select can be non correlated or correlated.In addition, searched UPDATE or DELETE statements can be self referencing.That is you can update or delete rows from a table referenced in the inner select.However, the statements cannot be a positioned update or delete as a result of selecting rows with the FOR UPDATE OF clause in the cursor definition and WHERE CURRENT OF in UPDATE or DELETE.If this is attempted, a 1.SQLCODE is returned.You can use a correlated subselect as a condition.For example, the STATUS column can be set to the number of times a supplier is used on a job.SELECT COUNT. FROM SPJ AS SPJ1.WHERE S1. SN SPJ1.SN. It is also possible to update a table referenced in the inner select provided that the column in the inner select is not the same column in the outer portion of the statement V7.If more than one row qualifies in a correlated subselect using IN, ANY, SOME, and EXISTS, RIDs of qualifying rows and the column value for updates are written to a work file.Rows are reread using RIDs in the work file and the updates are applied.Recall that if more than one row qualifies in a non correlated subselect, an 8.SQLCODE is returned.The same principles applies to deleting rows as updating rows based on the results of a subselect.That is you can delete rows from a table based on the results of a subselect.The following is an example of a self referencing DELETE statement that deletes rows from the SPJ table if the maximum number of parts allowed on any job is exceeded.The P9. 9 row contains the maximum QTY.The same principle applies to an UPDATE statement.DELETE FROM SPJ SPJ1.WHERE SPJ1. QTY. SELECT SPJ2.QTY. FROM SPJ SPJ2.WHERE SPJ1. SN SPJ2.SN. AND SPJ1. PN SPJ2.PN. AND SPJ2. PN P9.Keep in mind that a self referencing DELETE and UPDATE applies only to correlated subselects because of the need for two step processing to be discussed in the next section.UPDATE and DELETE statements based on the results of a correlated subselect that returns more than one row can be transformed to a join.An example is to set the S.STATUS 0 if S4 supplies 0 parts to any job in SPJ.WHERE SN S4. SELECT SPJ.SN no unique index on SPJ.SN. WHERE QTY 0. AND SPJ.SN S4. AND SPJ. SN S1.SN. Here is a second example that deletes JNs if a specific JN J5 is using 0 parts.DELETE FROM J AS J1.WHERE JN J5. WHERE QTY 0.AND SPJ. JN J5. AND SPJ.JN J1. JN. A nested loop join is often used when UPDATE and DELETE statements with a subselect are transformed to a join.This is true for the previous two examples.Two step processing for correlated UPDATE and DELETE statements makes it possible to do the transformation to a join.Step one consists of writing the RIDs of qualifying rows and the column value for updates to a work file.Step two consists of rereading the rows using the RIDs from the work file using list prefetch.Updates or deletes are applied after verifying that the row has not changed while retrieving RIDs and work file processing.This is true for all cases where list prefetch is used.The two step processing is required if more than one row qualifies in a correlated subselect using IN, ANY, SOME, and EXISTS.Another case is if the column being updated is also referenced in the WHERE clause of the update or is used in the correlation predicate of the inner select.The two step processing is always required for a correlated DELETE statement.Keep in mind that if more than one row qualifies in a non correlated subselect, 8.SQLCODE is returned and there is no further processing.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |