Comparison Operators

The Historian OLE DB Provider supports the use of comparison symbols within SQL statements. The following table outlines the comparison operators supported.

Table 1. Expression Comparisons
Comparison SymbolMeaning
<Less Than
>Greater Than
<=Less Than or Equal
>=Greater Than or Equal
=Equal
!=Not Equal
!>Not Greater Than
!<Not Less Than
BETWEEN x AND yBetween the values x and y inclusive, where x and y are numeric values

The Historian OLE DB Provider does not support a literal on the left side of the comparison operator. For example, this statement would fail:

SELECT DISTINCT tagname FROM ihRawData WHERE 50>Value
But this statement succeeds, since the Value column is to the left of the > operator:
SELECT DISTINCT tagname FROM ihRawData WHERE Value>50

The following examples show other possible uses of these comparison symbols in SELECT statements.

Example 1: Retrieve Tags with a High EGU Greater Than 300

SELECT DISTINCT tagname, loengineeringunits, hiengineeringunits
FROM ihTags WHERE hiengineeringunits > 300

Example 2: Retrieve Tags with a Specific Description

SELECT tagname, description FROM ihTags WHERE description = "aa"

Example 3: Retrieve All Samples Where the Value Exceeds Query Supplied Values

SELECT timestamp, tagname, value FROM ihRawData WHERE samplingmode=rawbytime AND value>75

Example 4: Retrieve All Samples Where the Value is Between Query Supplied Values

SELECT timestamp, tagname, value FROM ihRawData WHERE samplingmode=lab AND value BETWEEN 25 AND 75

Example 5: Retrieve All Tag Names Starting with an A or B

SELECT * FROM ihtags WHERE tagname < 'C'