How Does Parameter Order Affect Query Results in OleDbCommand?

OleDbCommand Parameters Order and Priority

When executing queries with parameters in OleDbCommand, it is crucial to understand the order and priority of the parameters. Despite the use of named parameters, OleDbCommand does not support named parameters for SQL statements or stored procedures when CommandType is set to Text.

As a result, the question mark (?) placeholder must be used in the query. The order in which these placeholders appear in the query corresponds to the order in which OleDbParameter objects are added to the OleDbParameterCollection.

Consider the following query:

SELECT * FROM tblSomeThing WHERE id = @id AND debut = @dtDebut AND fin = @dtFin

To execute this query correctly, the parameters must be added to the OleDbCommand as follows:

cmd.Parameters.Add("@id", OleDbType.Integer).Value = idSociete;
cmd.Parameters.Add("?dtDebut", OleDbType.Date).Value = dateTraitementDebut;
cmd.Parameters.Add("?dtFin", OleDbType.Date).Value = dateTraitementFin;

Note that "@dtDebut" and "@dtFin" have been replaced with "?dtDebut" and "?dtFin" respectively. The question mark placeholders must match the order in which they appear in the query.

In the debugging example mentioned, the parameters were switched when adding them to the collection. This resulted in no results being returned because the OleDbCommand executed the query with the parameters in the order they were added, not the order specified in the query.

Therefore, it is essential to pay attention to the order and priority of parameters in OleDbCommand when using question mark placeholders. Failure to do so can lead to unexpected results or errors.

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