SQL Operations
The basic SQL operations supported include:
• String concatenation operations
• Assignment operations
• Arithmetic operations
• Date(ingresdate) operations
String Concatenation Operations
To concatenate strings, use the + operator.
For example:
'This ' + 'is ' + 'a ' + 'test.'
gives the value:
'This is a test.'
Also, the concat function can be used to concatenate strings. For details, see
String Functions (see
String Functions).
Assignment Operations
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.
• If the data types are not the same, comparable data types are converted.
• If the data types are not comparable, convert the assignment value into a type that is the same or comparable with the receiving column or variable.
For information about the type conversion functions, see
Default Type Conversion (see
Default Type Conversion).
Character String Assignments
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.
String Truncation
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:
• COPY
• CREATE TABLE...SELECT
• INSERT
• UPDATE
Numeric Assignments
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 client or the DBMS Server can truncate leading zeros, or all or part of the fractional part of a number if necessary. If truncation of the non-fractional part of a value (other than leading zeros) is necessary, an overflow error results. OpenROAD does not report numeric overflow errors.
• If the receiving column or variable specifies more digits to the right of the decimal point than is present in the assignment value, the assignment value is padded with trailing zeros.
• When a float, float4, decimal, or money value is assigned to an integer column or variable, the fractional part is truncated.
• When a decimal value with a scale greater than two is assigned to a money column or variable, the fractional value is rounded.
• Character data is subject to numeric syntax checks if assigned in a numeric or money context.
Date(ingresdate) Assignments
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 (see
Date and Time Display).
Logical Key Assignments
There are two types of logical keys:
TABLE_KEY
This type is comparable only with another TABLE_KEY or a char that has a length of 8 bytes (char(8)).
OBJECT_KEY
This type is comparable only with another OBJECT_KEY or a char that has a length of 16 bytes (char(16)).
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 (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:
INSERT INTO test (tablekey) VALUES (TABLE_KEY(X'0000000000000001'));
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:
INSERT INTO test (tablekey) VALUES (TABLE_KEY('abc'));
Null Value Assignments
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.
Arithmetic Operations
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 (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.
Default Type Conversion
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:
• money
• float4
• float
• decimal
• integer8
• integer
• smallint
• integer1
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:
(job.Lowsal + 1000) * 12
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).
Arithmetic Operations on Decimal Data Types
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:
1.234 + 567.89
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.
Date/Time Arithmetic
The following arithmetic is supported for date/time data types.
Note: Notes:
• DATE(INGRESDATE) can store both absolute values and interval values.
• 'interval type' can be any of the ANSI forms or the DATE(INGRESDATE) interval form
• 'absolute type' is a non-interval form
Operators that return absolute date forms:
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.
Operators used with intervals:
The combining rule is, if an operand is DATE(INGRESDATE), the result will also be DATE(INGRESDATE).
Date(ingresdate) Interval Arithmetic
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:
date('6 days') + date('5 hours')
yields, 6 days 5 hours, while:
date('4 years 20 minutes') + date('6 months 80 minutes')
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:
date('2 days') - date('4 hours')
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:
num_days = int4(interval('days', 'today' - date('1/1/00')))
To convert the interval back to a date:
(date('1/1/00') + concat(char(num_days), ' days'))
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:
date('1-feb-98') + '1 month'
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:
create table dtest (dcolumn date);
insert into dtest (dcolumn) values (date('today'));
If the contents of the date column is selected using the following query:
select dcolumn from dtest;
a date with no time is returned. For example:
09-aug-2001
If date arithmetic is used to adjust the value of the date column, the values in the column acquire a time. For example:
update dtest set dcolumn=dcolumn-date('1 hour');
select dcolumn from dtest;
returns the value:
08-aug-1998 23:00:00
Date(ingresdate) Comparisons
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.
Operator Coercion Rules
The implicit coercion rules for operators are as follows:
1. Generally, where a numeric type is required, a string type can be supplied. This is the case for c, text, char, varchar, nchar, and nvarchar. If the character data turns out not to be numeric in form, a conversion error will occur.
2. Generally, where a string type is required, a numeric type can be supplied. This is the case for all integers, decimal, and all floats.
3. When an operator combines two values of the same data class, string or number, then the following precedence, shown from highest to lowest, is followed:
nchar
nvarchar
c
text
money
char
varchar
float
decimal
int
The resolver coerces to types that retain data without over inflating it. For example, coercion of nchar to char is avoided due to loss of richness of data form or collation. Similarly, coercing to a long type might work but would be grossly inefficient. Associated with this is the practical notion that most operators have a type themselves, some are arithmetic (*, /, and so on) and some are string (LIKE and so on).
4. The exception to Rule 3 is the "+" operator, which is an arithmetic operator as well as a concatenation operator for strings. The two modes coexist, but if a number is added to a string, then the result type is a number.
5. Mixed type comparisons between character and numeric data are virtually coerced into Numeric String data before being compared.