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# pgScript Scripting Language Reference

## Overview

pgScript is composed of pgScript commands:

    pgScript command
        : Regular PostgreSQL SQL Command (SELECT INSERT CREATE ...)
        | Variable declaration or assignment (DECLARE SET)
        | Control-of-flow structure (IF WHILE)
        | Procedure (ASSERT PRINT LOG RMLINE)

Command names (SELECT, IF, SET, ...) are case-insensitive and must be ended with a semi-column `;`. Identifiers are case-sensitive.

## Examples

### Batch table creations

    DECLARE @I, @T; -- Variable names begin with a @
    SET @I = 0; -- @I is an integer
    WHILE @I &lt; 20
    BEGIN
       SET @T = 'table' + CAST (@I AS STRING); -- Casts @I
       CREATE TABLE @T (id integer primary key, data text);

       SET @I = @I + 1;
    END

### Insert random data

    DECLARE @I, @J, @T, @G;
    SET @I = 0;
    SET @G1 = INTEGER(10, 29, 1); /* Random integer generator
                                 Unique numbers between 10 and 29 */
    SET @G2 = STRING(10, 20, 3); /* Random string generator
                                 3 words between 10 and 20 characters */
    WHILE @I &lt; 20
    BEGIN
        SET @T = 'table' + CAST (@I AS STRING);

    SET @J = 0;
        WHILE @J &lt; 20
        BEGIN
            INSERT INTO @T VALUES (@G1, '@G2');
            SET @J = @J + 1;
        END

    SET @I = @I + 1;
    END

### Batch table deletions

    DECLARE @I, @T; -- Declaring is optional
    SET @I = 0;
    WHILE 1 -- Always true
    BEGIN
        IF @I &gt;= 20
          BREAK; -- Exit the loop if @I &gt; 20

     SET @T = 'table' + CAST (@I AS STRING);
        DROP TABLE @T;

     SET @I = @I + 1;
    END

### Print information on screen

    SET @PROGR@M#TITLE = 'pgScript';
    PRINT '';
    PRINT @PROGR@M#TITLE + ' features:';
    PRINT '';
    PRINT '  * Regular PostgreSQL commands';
    PRINT '  * Control-of-flow language';
    PRINT '  * Local variables';
    PRINT '  * Random data generators';</pre>

## SQL Commands

You can run ANY PostgreSQL query from a pgScript EXCEPT those ones:

    BEGIN;
    END;

This is because BEGIN and END are used for delimiting blocks. Instead use:

    BEGIN TRANSACTION;
    END TRANSACTION;

For a list of PostgreSQL commands: http://www.postgresql.org/docs/8.3/interactive/sql-commands.html

## Variables

There are two main types of variables : simple variables and records (result sets composed of lines and columns).

Variable names begin with a `@` and can be composed of letters, digits, `_`, `#`, `@`.

Variable type is guessed automatically according to the kind of value it contains. This can be one of: number (real or integer), string, record.

### Simple variables

#### Simple variable declaration

Declaring simple variable is optional:

    DECLARE @A, @B;
    DECLARE @VAR1;

#### Simple variable affectation

This is done with the SET command. The variable type depends on the value assigned to this variable:

    SET @A = 1000, @B = 2000;   -- @A and @B are <strong>integer numbers**
    SET @C = 10e1, @D = 1.5;    -- @C and @D are <strong>real numbers**
    SET @E = 'ab', @F = 'a''b'; -- @E and @F are <strong>strings**
    SET @G = "ab", @H = "a\"b"; -- @G and @H are <strong>strings**

An uninitialized variable defaults to an empty string. It is possible to override variables as many times as wanted:

    PRINT @A;      -- Prints an empty string
    SET @A = 1000; -- @A is initialized an integer
    PRINT @A;      -- Prints 1000
    SET @A = 'ab'; -- @A becomes a string
    PRINT @A;      -- Prints ab

#### Data generators

Data generators allows users to generate random values. There are various types of generators, each one producing different type of data. A variable initialized with a data generator behaves like a regular simple variable except that it has a different value each time it is used:

    SET @A = INTEGER(100, 200);
    PRINT @A; -- Prints an integer between 100 and 200
    PRINT @A; -- Prints another integer between 100 and 200

A variable can contain a generator but its type is one of: number (real or integer), string. For a list of available generators and their associated type, see generators.

### Records

#### Record declaration

Declaring a record is required. A name for each column must be specified even if they will not be used anymore afterwards:

    DECLARE @R1 { @A, @B }, @R2 { @A, @C }; -- Two records with two  columns
    DECLARE @R3 { @A, @B, @C, @D };         -- One record  with four columns

The number of lines is dynamic: see the next section.

#### Record affectation

To access a specific location in a record, one must use the line number (starts at 0) and can use either the column name (between quotes) or the column number (starts at 0). This specific location behaves like a simple variable. Note that a record cannot contain a record:

    SET @R1[0]['@A'] = 1; -- First line &amp; first column
    SET @R1[0][0] = 1;    -- Same location
    SET @R1[4]['@B'] = 1; -- Fifth line &amp; second column
    SET @R1[0][1] = 1;    -- Same location

In the above example, three empty lines are automatically inserted between the first and the fifth. Using an invalid column number or name results in an exception.

Specific location can be used as right values as well. A specific line can also be used as right value:

    SET @R1[0][0] = @R3[0][1], @A = @R2[0][0]; -- Behaves like simple variables
    SET @A = @R1[1]; -- @A becomes a record which is the first line of @R1

Remember that `SET @R1[0][0] = @R2` is impossible because a record cannot contain a record.

It is possible to assign a record to a variable, in this case the variable does not need to be declared:

    SET @A = @R3; -- @A becomes a record because it is assigned a record

#### SQL queries

Any SQL query executed returns a record. If the query is a `SELECT` query then it returns the results of the query. If it is something else then it returns a one-line record (`true`) if this is a success otherwise a zero-line record (`false`):

    SET @A = SELECT * FROM table;   -- @A is a record with the results of the query
    SET @B = INSERT INTO table ...; -- @B is a one-line record if the query succeeds

#### Record functions

See function2.

### Cast

It is possible to convert a variable from one type to another with the cast function:

    SET @A = CAST (@B AS STRING);
    SET @A = CAST (@B AS REAL);
    SET @A = CAST (@B AS INTEGER);
    SET @A = CAST (@B AS RECORD);

When a record is converted to a string, it is converted to its flat representation. When converted to a number, the record is first converted to a string and then to a number (see string conversion for more details).

When a number is converted to a string, it is converted to its string representation. When converted to a record, it is converted to a one-line-one-column record whose value is the number.

When a string is converted to a number, if the string represents a number then this number is returned else an exception is thrown. When converted to a record, either the program can find a record pattern in the string or it converts it to a one-line-one-column record whose value is the string. A record pattern is:

    SET @B = '(1, "abc", "ab\\"")(1, "abc", "ab\\"")'; -- @B is a string
    SET @B = CAST (@B AS RECORD); @B becomes a two-line-three-column record

Remember a string is surrounded by simple quotes. Strings composing a record must be surrounded by double quotes which are escaped with `\\` (we double the slash because it is already a special character for the enclosing simple quotes).

### Operations

Operations can only be performed between operands of the same type. Cast values in order to conform to this criterion.

Comparisons result in a number which is 0 or 1.

#### Strings

Comparisons: `= <> > < <= >= AND OR`

Concatenation: `+`

    SET @B = @A + 'abcdef'; -- @A must be a string and @B will be a string

Boolean value: non-empty string is `true`, empty string is `false`

Inverse boolean value: `NOT`

Case-insensitive comparison: `~=`

#### Numbers

Comparisons: `= <> > < <= >= AND OR`

Arithmetic: `+ - * / %`

    SET @A = CAST ('10' AS INTEGER) + 5; -- '10' string is converted to a number

Boolean value: 0 is `false`, anything else is `true`

Inverse boolean value: `NOT` (note that `NOT NOT 10 = 1`)

An arithmetic operation involving at least one real number gives a real number as a result:

    SET @A = 10 / 4.; -- 4. is a real so real division: @A = 2.5
    SET @A = 10 / 4;  -- 4 is an integer so integer division: @A = 2

#### Records

Comparisons: `= <> > < <= >= AND OR`

Boolean value: zero-line record is `false`, anything else is `true`

Inverse boolean value: `NOT`

Comparisons for records are about inclusion and exclusion. Order of lines does not matter. `<=` means that each row in the left operand has a match in the right operand. `>=` means the opposite. `=` means that `<=` and `>=` are both true at the same time...

Comparisons are performed on strings: even if a record contains numbers like `10` and `1e1` we will have `'10' <> '1e1'`.

## Control-of-flow structures

### Conditional structure

    IF condition
    BEGIN
        pgScript commands
    END
    ELSE
    BEGIN
        pgScript commands
    END

pgScript commands are optional. BEGIN and END keywords are optional if there is only one pgScript command.

### Loop structure

    WHILE condition
    BEGIN
        pgScript commands
    END

pgScript commands are optional. BEGIN and END keywords are optional if there is only one pgScript command.

BREAK ends the enclosing WHILE loop, while CONTINUE causes the next iteration of the loop to execute. RETURN behaves like BREAK:

    WHILE condition1
    BEGIN
        IF condition2
        BEGIN
            BREAK;
        END
    END

### Conditions

Conditions are in fact results of operations. For example the string comparison `'ab' = 'ac'` will result in a number which is `false` (the equality is not true):

    IF 'ab' ~= 'AB' -- Case-insensitive comparison which result in 1 (true) which is true
    BEGIN
        -- This happens
    END

    IF 0 -- false
    BEGIN
        -- This does **not** happen
    END
    ELSE
    BEGIN
        -- This happens
    END

    WHILE 1
    BEGIN
        -- Infinite loop: use BREAK for exiting
    END

It is possible to the result of a SQL SELECT query directly as a condition. The query needs to be surrounded by parenthesis:

    IF (SELECT 1 FROM table)
    BEGIN
        -- This means that table exists otherwise the condition would be false
    END

## Additional functions and procedures

### Procedures

Procedures do not return a result. They must be used alone on a line and cannot be assigned to a variable.

#### Print

Prints an expression on the screen:

    PRINT 'The value of @A is' + CAST (@A AS STRING);

#### Assert

Throws an exception if the expression evaluated is false:

    ASSERT 5 &gt; 3 AND 'a' = 'a';

#### Remove line

Removes the specified line of a record:

    RMLINE(@R[1]); -- Removes @R second line

### Functions

Functions do return a result. Their return value can be assigned to a variable, like the `CAST` operation.

#### Trim

Removes extra spaces surrounding a string:

    SET @A = TRIM(' a '); -- @A = 'a'</pre>

#### Lines

Gives the number of lines in a record:

    IF LINES(@R) &gt; 0
    BEGIN
        -- Process
    END

#### Columns

Gives the number of columns in a record:

    IF COLUMNS(@R) &gt; 0
    BEGIN
        -- Process
    END

## Random data generators

### Overview of the generators

One can assign a variable (SET) with a random data generators. This means each time the variable will be used it will have a different value.

However the variable is still used as usual:

    SET @G = STRING(10, 20, 2);
    SET @A = @G; -- @A will hold a random string
    SET @B = @G; -- @B will hold another random string
    PRINT @G,    -- This will print another third random string

### Sequence and seeding

Common parameters for data generators are sequence and seed.

sequence means that a sequence of values is generated in a random order, in other words each value appears only once before the sequence starts again: this is useful for columns with a `UNIQUE` constraint. For example, this generator:

    SET @G = INTEGER(10, 15, 1); -- 1 means generate a sequence

It can generate such values:

    14 12 10 13 11 15 14 12 10 13 11

Where each number appears once before the sequence starts repeating.

sequence parameter must be an integer: if it is 0 then no sequence is generated (default) and if something other than 0 then generate a sequence.

seed is an integer value for initializing a generator: two generators with the same parameters and the same seed will generate exactly the same values.

seed must be an integer: it is used directly to initialize the random data generator.

### Data generators

Optional parameters are put into brackets:

    Generator
     : INTEGER ( min, max, [sequence], [seed] );
     | REAL ( min, max, precision, [sequence], [seed] );
     | DATE ( min, max, [sequence], [seed] );
     | TIME ( min, max, [sequence], [seed] );
     | DATETIME ( min, max, [sequence], [seed] );
     | STRING ( min, max, [nb], [seed] );
     | REGEX ( regex, [seed] );
     | FILE ( path, [sequence], [seed], [encoding] );
     | REFERENCE ( table, column, [sequence], [seed] );

#### Integer numbers

    INTEGER ( min, max, [sequence], [seed] );
    INTEGER ( -10, 10, 1, 123456 );

`min` is an integer, `max` is an integer, `sequence` is an integer and `seed` is an integer.

#### Real numbers

    REAL ( min, max, precision, [sequence], [seed] );
    REAL ( 1.5, 1.8, 2, 1 );

`min` is a number, `max` is a number, `precision` is an integer that indicates the number of decimals (should be less than 30), `sequence` is an integer and `seed` is an integer.

#### Dates

    DATE ( min, max, [sequence], [seed] );
    DATE ( '2008-05-01', '2008-05-05', 0 );

`min` is a string representing a date, `max` is a string representing a date, `sequence` is an integer and `seed` is an integer.

#### Times

    TIME ( min, max, [sequence], [seed] );
    TIME ( '00:30:00', '00:30:15', 0 );

`min` is a string representing a time, `max` is a string representing a time, `sequence` is an integer and `seed` is an integer.

#### Timestamps (date/times)

    DATETIME ( min, max, [sequence], [seed] );
    DATETIME ( '2008-05-01 14:00:00', '2008-05-05 15:00:00', 1 );

`min` is a string representing a timestamp, `max` is a string representing a timestamp, `sequence` is an integer and `seed` is an integer.

#### Strings

    STRING ( min, max, [nb], [seed] );
    STRING ( 10, 20, 5 );

`min` is an integer representing the minimum length of a word, `max` is an integer representing the maximum length of a word, `nb` is an integer representing the number of words (default: `1`) and `seed` is an integer.

In the above example we generate 5 words (separated with a space) whose size is between 10 and 20 characters.

#### Strings from regular expressions

    REGEX ( regex, [seed] );
    REGEX ( '[a-z]{1,3}@[0-9]{3}' );

`regex` is a string representing a simplified regular expressions and `seed` is an integer.

Simplified regular expressions are composed of:

- Sets of possible characters like `[a-z_.]` for characters between `a` and `z` + `_` and `.`
- Single characters

It is possible to specify the minimum and maximum length of the preceding set or single character:

- `{min, max}` like `{1,3}` which stands for length between `1` and `3`
- `{min}` like `{3}` which stands for length of `3`
- Default (when nothing is specified) is length of `1`

Note: be careful with spaces because `'a {3}'` means one `a` followed by three spaces because the `3` is about the last character or set of characters which is a space in this example.

If you need to use `[` `]` `\` `{` or `}`, they must be escaped because they are special characters. Remember to use double backslash: `'\\[{3}'` for three `[`.

#### Strings from dictionary files

    FILE ( path, [sequence], [seed], [encoding] );
    FILE ( 'file.txt', 0, 54321, 'utf-8' );

`path` is a string representing the path to a text file, `sequence` is an integer, `seed` is an integer and `encoding` is a string representing the file character set (default is system encoding).

This generates a random integer between 1 and the number of lines in the file and then returns that line. If the file does not exist then an exception is thrown.

`encoding` supports the most known encoding like utf-8, utf-16le, utf-16be, iso-8859-1, ...

#### Reference to another field

    REFERENCE ( table, column, [sequence], [seed] );
    REFERENCE ( 'tab', 'col', 1 );

`table` is a string representing a table, `column` is a string representing a column of the table, `sequence` is an integer and `seed` is an integer.

This is useful for generating data to put into foreign-key-constrained columns.

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