6.1.2 Rules for separators : Hitachi Advanced Database SQL Reference

(1) About separators

When writing SQL statements, you need to put separators between two keywords, or between keywords and names, and so on. Separators include the following:

Spaces

The following white space characters are treated as spaces:
- Space
- CR (carriage return): Return
- NL (new line): Line break
- Tab
Comments

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(2) Where separators must be inserted

Separators must be inserted in the following places:

Between two keywords
Between a keyword and a name
Between two names
Between a keyword and a numeric value
Between a name and a numeric value

Examples of where separators must be inserted are shown in the following figure.

Figure 6‒2: Examples of where separators must be inserted

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(3) Where separators cannot be inserted

Separators cannot be inserted in the following places:

Inside a keyword
Inside a name that is not enclosed in double quotation marks (")
After the opening double quotation mark (") that encloses a name
Before the closing double quotation mark (") that encloses a name
Inside a numeric literal (except after the sign specified at the beginning)
Between the X and the following ' in the hexadecimal-format binary literal representation X'...'
Between the B and the following ' in the binary-format binary literal representation B'...'
Inside an operator (inside a comparison operator consisting of two characters)

Examples of where separators cannot be inserted are shown in the following figure.

Figure 6‒3: Examples of where separators cannot be inserted

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(4) Where separators can be inserted

Separators can be inserted in the following places:

In places not prohibited under (3) Where separators cannot be inserted above, as well as before and after the following special characters:

, . -+ * '" ( )< > = ^ ! ? tab NL CR space

Examples of where separators can be inserted are shown in the following figure.

Figure 6‒4: Examples of where separators can be inserted

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(5) Comments

You can add a comment at any location in an SQL statement where a separator can be inserted. Comments are illustrated in the example below.

Example

SELECT "C1","C2" FROM "T1"    /* comment1 */
    ORDER BY "C1" ASC         /* comment2 */

The underlined portions are comments. Everything between the /* and the */ is considered part of the comment.

When writing comments, the following guidelines must be observed:

A comment cannot be placed inside an identifier or character string literal.
Comments cannot be nested.

Example
```
SELECT * FROM  "T1" /* /* comment1 */ comment2 */
```
Specifying nested comments as shown above results in a syntax error.
If the /* and */ are enclosed in double quotation marks (") or single quotation marks ('), they are not treated as defining a comment.

Example
```
SELECT * FROM "T1" WHERE "C1"='/* comment */'
```
The underlined portion above is treated as a character string literal rather than a comment.
Note that a character string that begins with /*>> and ends with <<*/ is not treated as a comment.

Example
```
SELECT * FROM "T1" /*>> WITHOUT INDEX <<*/
```
In the preceding example, the underlined portion is treated as an index specification rather than a comment. For details about index specifications, see 7.14 Index specification.

However, a comment can appear within the index specification enclosed in /*>> and <<*/.

Example
```
SELECT * FROM "T1" /*>> WITHOUT INDEX /* WITH INDEX(INDEXNAME)*/ <<*/
```
The underlined portion above is treated as a comment. When processed, it is equivalent to the following SQL statement:
```
SELECT * FROM "T1" /*>> WITHOUT INDEX <<*/
```
Note that a character string that begins with /*>> and ends with <<*/ cannot be specified within a comment. For example, it is impossible to include an index specification in a comment.

Example
```
SELECT * FROM "T1" /* /*>> WITHOUT INDEX <<*/ */
```
In the preceding example, an index specification (the underlined portion) appears within a comment. Therefore, this SQL statement results in a syntax error.

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