Basic Language Elements

Examples

-- This is a comment

SELECT * FROM dual;

-- Display the number of rows of table dual
SELECT count(*) FROM dual;

SELECT avg(salary) -- Average salary
FROM staff         -- From table staff
WHERE age>50;      -- Limitation to over 50 years old

/* Any number of comment rows can be
inserted between the delimiters
*/
SELECT * FROM dual;

SELECT /*This section is not evaluated!*/ * FROM dual;

Regular Identifiers

Regular identifiers are stated without quotation marks. As defined in the SQL standard, Exasol only allows a subset of the unicode characters. The first letter is more restricted than the following ones. Detailed lists of characters in each of the specified classes are defined in the Unicode standard.

• First Letter: All letters of unicode classes Lu (upper-case letters), LI (lower-case letters), Lt (title-case letters), Lm (modifier letters), Lo (other letters), and Nl (letter numbers).
• Following Letters: The classes of the first letter (aforementioned) and additionally all letters of unicode classes Mn (non-spacing marks), Mc (spacing combination marks), Nd (decimal numbers), Pc (connectors punctuations), Cf (formatting codes), and the unicode character U+00B7 (middle dot).

Regarding the simple ASCII character set, these rules denote that a regular identifier may start with letters of the set {a-z, A-Z} and may further contain letters of set {a-z, A-Z, 0-9,_}.

A further restriction is that a reserved word cannot be used as a regular identifier.

If you want to use characters that are prohibited for regular identifiers, you can use Delimited Identifiers. For example, if you want to use the word table as identifier, you have to quote it ("table"), since it is a reserved word.

Regular identifiers are always stored in upper case. They are not case-sensitive. Therefore, in the below example, the two identifiers ABC and abc are equal.

Regular identifiers are stored in upper case.

Examples

Delimited Identifiers

These identifiers are names enclosed in double quotation marks. Any characters can be used within the quotation marks except the dot ('.'). In the case of users and roles, you are allowed to use the dot ('.'), for example, in email addresses. This is possible because users and roles do not conflict with the schema-qualified objects. For more information, refer to the Schema-Qualified Names section.

When you want to use double quotation marks in the name, you must include two double quotation marks next to one another. For example, "ab""c" indicates the name ab"c.

Note: Except in users and roles, delimited identifiers in quotation marks are always case-sensitive when stored in the database.

Examples

Schema-Qualified Names

Database objects, when called via schema-qualified names, the names are separated with a period. This enables access to schema objects which are not located in the current schema.

Examples

SELECT my_column FROM my_schema.my_table;
SELECT "my_column" FROM "my_schema"."my_table";
SELECT my_schema.my_function(my_column) from my_schema.my_table;

Reserved Words

Some reserved words cannot be used as regular identifiers. For example, the keyword SELECT. It is a reserved word. If you need to create a table with the name SELECT, this is only possible if the name is within double quotation marks. Therefore, SELECT as a table name is different from a table name such as Select or seLect.

A list of reserved words in Exasol can be found in the EXA_SQL_KEYWORDS system table.

The compiled code for PCRE uses an offset of 2-bytes by default (always stored in big-endian order). These are used, for example, to link from the start of a subpattern to its alternatives and its end. The use of 2 bytes per offset limits the size of the compiled pattern to 64K.

Examples

In the description of the corresponding scalar functions and predicates, you can find examples of regular expressions within SQL statements. The following examples demonstrate the general expressions: 

Note: These example expressions are simplified to provide clarity. The productive expressions, for example, identifying valid email addresses are much more complex.

Pattern Elements

You can use the following elements in regular expressions:

SELECT 
    col1, 
    col1 regexp_like '(?i:hello)world' as match_flag
FROM 
    values 'helloworld', 'Helloworld', 'HellOworld', 'helloWorld', 'helloWORLD' as t1(col1);