![]() ![]() Consider a sample: select * from myTable where !isCustomer AND debit > 5000 OR discount > 5 ![]() When there are many of them, one might ignore the fact that operators have a precedence (in order (), NOT, AND, OR) and think the interpretation would be done left to right in a chain. One pitfall that catches newbies is that, sometimes you might need multiple checks, say in an SQL query, which are connected with AND, OR operators. * the whole expression would be true, thus the expression after OR * without any error because m.llProcess true means * (VFP is dynamic and there is no compile time check) * However we could use such an expression in an if and get no error It would complain operator/operand type mismatch. A sample follows: ? 1 = '2' & An obvious error. That is, if the first part of the check satisfies the whole result, rest of the expression is not even interpreted. In VFP, logical expresssions are evaluated in a shortcut fashion. If ( m.llOld AND !m.llEmail ) & Same as (m.llOld AND NOT m.llEmail) Local llOld, llEmail & any variable declaration implicitly initializes the variable as. You cannot choose to use F and T instead. You can still use them if you like to, but AND, OR, NOT is simpler and cleaner.įor false and true, you have to use. Historically, NOT, AND, OR are written as. NOT or ! has no difference.Ĭheck for inequality. Logical operators in VFP, in their order of precedence are: Operator ![]()
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