2.4 Expressions

Although all DBTools.h++ access libraries are implemented through a common interface, there are differences in the parameters that must be passed to certain expressions. The following section outlines the differences in the Oracle8 access library.

2.4.1 Global Functions

Table 4 lists restrictions on the global functions associated with RWDBExpr.

Table 4 -- Restrictions on the use of global functions

Function	Restrictions
`rwdbAvg(const RWDBExpr&)`	None. Corresponds to: `AVG(expr)`
`rwdbCast(const RWDBExpr&, const RWDBValue&)`	See Section 2.4.2.
`rwdbCast(const RWDBExpr&, const RWDBValue&, const RWDBExpr&)`	See Section 2.4.2.
`rwdbCast(const RWBDExpr&, const RWDBValue&, const RWDBExpr&, const RWDBExpr&)`	See Section 2.4.2.
`rwdbCharLength(const RWDBExpr&)`	None. Corresponds to: `LENGTH(expr)`
`rwdbCount()`	None. Corresponds to: `COUNT(*)`
`rwdbCount(const RWDBExpr&)`	None. Corresponds to: `COUNT(expr)`
`rwdbCountDistinct(const RWDBExpr&)`	None. Corresponds to: `COUNT(DISTINCT expr)`
`rwdbCurrentUser()`	None. Corresponds to: `USER`
`rwdbExists(const RWDBSelectorBase&)`	None. Corresponds to: `EXISTS sel`
`rwdbLower(const RWDBExpr&)`	None. Corresponds to: `LOWER(expr)`
`rwdbMax(const RWDBExpr&)`	None. Corresponds to: `MAX(expr)`
`rwdbMin(const RWDBExpr&)`	None. Corresponds to: `MIN(expr)`
`rwdbName(const RWCString&, const RWDBExpr&)`	None. Corresponds to: `string1 = expr0`
`rwdbPosition(const RWDBExpr&, const RWDBExpr&)`	None. Corresponds to: `instr(expr1, expr0)`
`rwdbSessionUser()`	None. Corresponds to: `USER`
`rwdbSubString(const RWDBExpr&, const RWDBExpr&)`	None. Corresponds to: `substr(expr0, expr1)`
`rwdbSubString(const RWDBExpr&, const RWDBExpr&, const RWDBExpr&)`	None. Corresponds to: `SUBSTR(expr0, expr1, expr2)`
`rwdbSum(const RWDBExpr&)`	None. Corresponds to: `SUM(expr)`
rwdbSystemDateTime()	None. Corresponds to: `SYSDATE`
`rwdbSystemUser()`	None. Corresponds to: `USER`
`rwdbTrimLeading(const RWDBExpr&, const RWDBExpr&)`	None. Corresponds to: `LTRIM(expr1, expr0)`
`rwdbTrimTrailing(const RWDBExpr&, const RWDBExpr&)`	None. Corresponds to: `RTRIM(expr1, expr0)`
`rwdbTrimBoth(const RWDBExpr&, const RWDBExpr&)`	None. Corresponds to: `LTRIM(RTRIM(expr1, expr0), expr0)`
`rwdbUpper(const RWDBExpr&)`	None. Corresponds to: `UPPER(expr)`

2.4.2 rwdbCast()

The predefined expression, rwdbCast(), allows an application to change the type of a value in the database to another type. For example, with rwdbCast() you can change a number to a character string. The parameters for rwdbCast() should be specified in the following ways:

Casting to a character string: rwdbCast(expression,"CHAR")
Casting to a number: rwdbCast(expression,"NUMBER")
Casting to a date: rwdbCast(expression,"DATE")

As shown in Table 4, there are also three-parameter and four-parameter versions of the rwdbCast() expression. These can also be used to provide optional format and language parameters for the TO_CHAR, TO_NUMBER, and TO_DATE conversion functions.