FireDAC Components for Dataflex

Build 20.0.7587

DELETE SELECT Statements

To perform multiple deletes in a single request to Dataflex, use the DELETE ... SELECT syntax to insert a temporary table of data into Dataflex. This works by first populating a temporary table with the data you are going to submit to Dataflex. Once you have all of the data you want to delete, the temporary table is then passed into the table you are inserting to.

Populate the Temporary Table

The temporary table you are populating is dynamic and is created at run time the first time you insert to it. Temporary tables are denoted by a # appearing in their name. When using a temporary table to delete, the temporary table must be named in the format [TableName]#TEMP, where TableName is the name of the table you are inserting to. For example:

INSERT INTO Accounts#TEMP (AccountId) VALUES ('AX1000001');
INSERT INTO Accounts#TEMP (AccountId) VALUES ('AX1000002');
INSERT INTO Accounts#TEMP (AccountId) VALUES ('AX1000003');

This creates a temporary table called Accounts#TEMP with one column and three rows of data. Since type cannot be determined on the temporary table itself, all values are stored in memory as strings. They are later converted to the proper type when they are submitted to the Accounts table.

Delete from the Actual Table

Once your temporary table is populated, it is now time to insert to the actual table in Dataflex. You can do this by performing a DELETE from the actual table and selecting the input data from the temporary table. For example:

DELETE FROM Accounts WHERE EXISTS SELECT AccountId FROM Accounts#TEMP

In this example, the full contents of the Accounts#TEMP table are passed into the Accounts table. This results in fewer requests being submitted to Dataflex since multiple deletes may be submitted with each request, which is much better for performance if you have many records to delete.

Results

The results of the query are stored in the LastResultInfo#TEMP temporary table. This table is cleared and repopulated the next time data is modified by passing in a temporary table. Please be aware that the LastResultInfo#TEMP table has no predefined schema. You need to check its metadata at run time before reading data.

Temporary Table Life Span

Temporary tables only last as long as the connection remains opened. When the connection to Dataflex is closed, all temporary tables are cleared, including the LastResultInfo#TEMP table.

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Build 20.0.7587