OpenROAD supports these operators:

The following sections describe these operators.

The arithmetic operators in OpenROAD combine numeric expressions into new expressions. These operators are listed in the following table:

The following are examples:

In addition to standard arithmetic, OpenROAD supports date arithmetic. For example, if start_date is a date field, OpenROAD can compute the result value for the following statement:

The precedence of operators in expressions is as follows (highest to lowest):

Operators are processed from left to right to control equal precedence.

For example, the following expression has a value of 14 because the multiplication operator (*) has precedence over the addition operator (+):

You can use parentheses to force alternate precedence. For example, placing parentheses around the expression from the previous example alters its value to 20:

Take care when dividing either a float variable into an integer literal constant or an integer literal constant into a float variable, as the result is of the float type but rounded down to the nearest integer.

The concatenation operator (+) joins string expressions together into new expressions, for example:

The logical operators AND, OR, and NOT join logical expressions into new expressions with a boolean value. The following truth tables show the result of comparisons made with these operators.

The order of precedence for these operators, from highest to lowest, is as follows:

You can use parentheses to change this order. In the following example:

OpenROAD first evaluates empnum and deptno and then evaluates status.

The following example illustrates the use of comparison and logical operators:

The newemployee frame is called only if both conditions are TRUE, that is, if the current value of empnum is greater than 0, and status has any value other than 3.

Boolean expressions yield the boolean values TRUE, FALSE, or (with nullable expressions) null. 4GL includes the logical operators AND, OR, and NOT, and the following comparison operators:

With null, the result of a comparison will be true, false, or null. The result of a comparison (except for a comparison of reference variables) is null when one or both operands of the expression are null.

In 4GL, the if and while statements and the where clause of query statements test the results of boolean expressions. For example, assume that status is a character field on a form. Whenever the boolean expression “status = 'n' ” is TRUE, the following statement calls the NewProject frame:

In if and while statements, if the result of an expression is null, the flow of control occurs exactly as if the boolean expression evaluates to FALSE. For examples, see Nulls in Expressions.

Reference variables may be compared, but only for equality, inequality, is null, or is not null. When comparing two reference variables that both contain null for equality (or inequality), the result is TRUE or FALSE, not null. Similarly, when comparing two reference variables only one of which contains null for equality, the result is FALSE.

An operator is a symbol that represents an action performed on one or more expressions.

There are three types of SQL operators:

Arithmetic operators are used to combine numeric expressions arithmetically to form other numeric expressions.

The following are the valid arithmetic operators (in descending order of precedence):

Unary operators group from right to left, while binary operators group from left to right. Use the unary minus (-) to reverse the algebraic sign of a value.

To force a desired order of evaluation, use parentheses. For example:

is an expression in which the parentheses force the addition operator (+) to take precedence over the multiplication operator (*).

Comparison operators compare two expressions. SQL includes the following comparison operators:

The <> operator can also be specified as != or ^=.

All comparison operators are of equal precedence.

The equal sign (=) also serves as the assignment operator in assignment operations (see Assignment Operations).

SQL has three logical operators, shown in order of precedence:

Use parentheses to change the order of evaluation. For example, the following expression:

is evaluated as:

When parentheses are used as follows:

OpenROAD evaluates (exprA or exprB) first, then uses the AND operator for the result with exprC. But in a SQL statement, it is sent to Ingres for evaluation.

Parentheses can also be used to change the default evaluation order of a series of expressions combined with the same logical operator. For example, the following expression:

is evaluated as:

To change this default left-to-right grouping, use parentheses as follows:

The parentheses direct OpenROAD to use the AND operator for exprB and exprC, then use the AND operator for that result with exprA.

The basic SQL operations supported include:

To concatenate strings, use the + operator.

For example:

gives the value:

Also, the concat function can be used to concatenate strings. For details, see String Functions.

An assignment operation places a value in a column or variable. Assignment operations occur during the execution of INSERT, UPDATE, FETCH, CREATE TABLE...AS SELECT, and embedded SELECT statements. Assignments can also occur within a database procedure.

When an assignment operation occurs, the data types of the assigned value and the receiving column or variable must either be the same or comparable.

For information about the type conversion functions, see Default Type Conversion.

All character types are comparable with one another and with integer and float types. Any character string can be assigned to any column or variable of character data type. A character string can also be assigned to a column or variable of integer or float type, as long as the content of the string is a valid numeric value. The result of the assignment depends on the types of the assignment string and the receiving column or variable.

If an attempt is made to insert a string value into a table column or variable that is too short to contain the value, the string is truncated.

String truncation also can occur as a result of the following statements:

All numeric types are compatible with one another and with character types. Money is compatible with all of the numeric and string data types.

Numeric assignments follow these rules:

The date data type is compatible with string data types if the value in the string is a valid representation of a date or time input format.

Absolute date or interval values can be assigned to an ingresdate variable. In addition, a string literal, a character string host variable, or a character string column value can be assigned to an date column if its value conforms to the valid input formats for Ingres dates or times.

When a date value is assigned to a character string, OpenROAD converts the date to the display format. For more information about date display formats, see Date and Time Display.

There are two types of logical keys:

If a logical key column is declared as SYSTEM_MAINTAINED, the DBMS Server assigns the values to that column. System maintained logical key columns cannot be updated. If a logical key column is declared as NOT SYSTEM_MAINTAINED, values must be assigned to the column.

In embedded SQL programs, if values are assigned using host variables, the host variables must be char(8)-comparable for TABLE_KEY columns, and char(16)-comparable variables for OBJECT_KEY columns.

Values can be assigned to logical keys, not system maintained, using a hex constant or a string literal. For information about the format of a hex constant, see String Literals.

Values assigned to TABLE_KEYs must be 8 bytes long. Values assigned to OBJECT_KEYs must be 16 bytes long. The following example inserts the value 1 into a TABLE_KEY column using a hex constant:

The previous statement inserts 7 bytes containing 0, followed by 1 byte containing 1. The value is explicitly converted to a table key using the table_key conversion function.

The following example assigns the value 'abc' (padded to 8 characters for data type compatibility) to a logical key column:

A null can be assigned to a column of any data type if the column was defined as a nullable column. A null can also be assigned to a host language variable if there is an indicator variable associated with the host variable.

To ensure that a null is not assigned to a column, use the IFNULL Function.

An arithmetic operation combines two or more numeric expressions using the arithmetic operators to form a resulting numeric expression. For details about arithmetic operators, see Arithmetic Operators.

Before performing any arithmetic operation, the participating expressions are converted to identical data types. After the arithmetic operation is performed, the resulting expression too has that storage format.

When two numeric expressions are combined, the data types of the expressions are converted to be identical; this conversion determines data type of the result. The expression having the data type of lower precedence is converted to the data type of the higher. The order of precedence among the numeric data types is, in highest-to-lowest order:

For example, in an operation that combines an integer and a floating point number, the integer is converted to a floating point number. If the operands are two integers of different sizes, the smaller is converted to the size of the larger. The conversions are done before the operation is performed.

The following table lists the data types that result from combining numeric data types in expressions:

For example, for the expression:

the first operator (+) combines a float4 expression (job.Lowsal) with a smallint constant (1000). The result is float4. The second operator (*) combines the float4 expression with a smallint constant (12), resulting in a float4 expression.

To convert one data type to another, use data type conversion functions (see Data Type Conversion Functions).

In expressions that combine decimal values and return decimal results, the precision (total number of digits) and scale (number of digits to the right of the decimal point) of the result can be determined, as shown in the following table:

For example, in the following decimal addition operation:

the scale and precision of the result is calculated as follows:

Precision = 7

Calculated as 3 (largest number of fractional digits) + 3 (largest number of non-fractional digits) + 1 = 7

Scale = 3

The first operand has the largest number of digits to the right of the decimal point.

Result:

0569.124

If exponentiation is performed on a decimal value, the resulting data type is float.

The following arithmetic is supported for date/time data types.

The combining rules are: If either term is date(ingresdate), the result will also be date(ingresdate); otherwise, the result will be the same as the absolute term.

The combining rule is, if an operand is DATE(INGRESDATE), the result will also be DATE(INGRESDATE).

Date(ingresdate) intervals can be added, subtracted, and divided, and can be multiplied or divided with a numeric expression. The following lists the results of date arithmetic:

When adding intervals, each of the units is added.

For example:

yields, 6 days 5 hours, while:

yields, 4 years 6 months 1 hour 40 minutes.

In the previous example, 20 minutes and 80 minutes are added and the result is 1 hour 40 minutes. 20 minutes plus 80 minutes equals 100 minutes, but this result overflows the minute time unit because there are 60 minutes in an hour. Overflows are propagated upward except when intervals are added. In the above example, the result is 1 hour 40 minutes. However, days are not propagated to months. For example, if 25 days is added to 23 days, the result is 48 days.

When intervals or absolute dates are subtracted, the result is returned in appropriate time units. For example, if the following subtraction is performed:

the result is 1 day 20 hours.

Date constants can be converted into numbers of days relative to an absolute date. For example, to convert today’s date to the number of days since January 1, 1900:

To convert the interval back to a date:

where num_days is the number of days added to the date constant.

Adding a month to a date always yields the same date in the next month. For example:

yields March 1.

If the result month has fewer days, the resulting date is the last day of the next month. For instance, adding a month to May 31 yields June 30, instead of June 31, which does not exist. Similar rules hold for subtracting a month and for adding and subtracting years.

Dates that are stored without time values can acquire time values as a result of date arithmetic. For example, the following SQL statements create a table with one date column and store today’s date (with no time) in the column:

If the contents of the date column is selected using the following query:

a date with no time is returned. For example:

If date arithmetic is used to adjust the value of the date column, the values in the column acquire a time. For example:

returns the value:

In comparisons, a blank (default) date(ingresdate) is less than any interval date(ingresdate). All interval dates(ingresdates) are less than all absolute date(ingresdates). Intervals are converted to comparable units before they are compared. For instance, before comparing date('5 hours') and date('200 minutes'), both the hours and minutes are converted to milliseconds internally before comparing the values. Dates(ingresdates) are stored in Greenwich Mean Time (GMT). For this reason, 5:00 PM Pacific Standard Time is equal to 8:00 PM Eastern Standard Time.

The implicit coercion rules for operators are as follows:

The like operator lets you compare two strings to see whether they resemble each other in specific ways. To use this operator, specify a pattern (a string of characters with special formatting characters) that specifies what the compared string must look like. If the string being compared is an instance of the pattern described by the pattern string, the expression evaluates to TRUE.

The syntax for the like operation is:

The is [not] null operator tests whether an expression is null. The syntax of this operator is:

The following code is an example: