Expression Overview with QrySelect
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| An expression to be used with a QrySelect within DCLDISKFILE is a logical expression consisting of one or more relational expressions optionally combined with the “&” (and) and “ | ” (or) operators. Since “&” has a higher priority than “ | ”, you can use parentheses to force the order in which the expression is evaluated. |
An expression is defined by a single or double quote, followed by any combination of characters, and terminated by a single or double quote. Note that a numeric field can be compared against numeric constants, and a character field must be compared against a quoted character constant .
Please note that if you want a double quote within a literal, you must include two quotes. For example, to assign to a character field the value <pre>He said “Come NOW!”.</pre>, The assignemnt would have to coded like this: <pre>phrase = “He said ““Come NOW!””.”</pre>
A relational expression consists of a field name, a relational operator and a constant or another field name.
The valid relational operators are:
| < | LT | Less Than |
| > | GT | Great Than |
| <= | LE | Less Than or Equal To |
| >= | GE | Greater Than or Equal To |
| = | EQ | Equal Condition |
| != | NE | Not Equal Condition |
| <> | NE | Not Equal Condition |
| & | AND | And |
| |, | OR | Or |
The example below ( Table 1 ) lists some example expressions, showing that if you want the expression to equal a particular character value, you must put double quotes around the value. Note that you do not need to specify quotes around a numeric value.
The result of the expression is derived from the fields X, Y and Z as listed in table 2 below.
Table 1
|
Expression |
Explanation | Result |
| "x = y" | The contents of field x = the contents of field y. | Record 2 |
| "x = ""y""" | The contents of field x = the character value Y. | Record 5 |
| "Z = 4" | The contents of field Z = the value 4. | Record 4 |
Table 2
|
Field X |
Field Y | Field Z |
| A | X | 1 |
| B | B | 2 |
| C | Y | 3 |
| X | C | 4 |
| Y | Z | 5 |
| Z | A | 6 |