DISTINCT

The Historian OLE DB Provider supports the use of DISTINCT in a SELECT statement. DISTINCT eliminates duplicate rows when all columns are equal. Floating-point values, however, may not compare as expected, depending on the precision. For example, if the numbers to the right of the decimal point are not equal for all values, similar columns are not eliminated. The columns must be exactly equal to be eliminated.

Example 1: Retrieve the Set of Unique Data Types Used in an Archive

SELECT DISTINCT datatype FROM ihtags

Example 2: Retrieve the Set of Tags With Raw Data Samples on a Specific Date

SELECT DISTINCT tagname FROM ihRawData WHERE samplingmode=rawbytime
AND timestamp>='11/28/2001' AND timestamp<='11/29/2001'