73 lines
2.5 KiB
Markdown
73 lines
2.5 KiB
Markdown
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---
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layout: default
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title: Identifiers
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parent: Piped processing language
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nav_order: 7
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---
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# Identifiers
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An identifier is an ID to name your database objects, such as index names, field names, aliases, and so on.
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OpenSearch supports two types of identifiers: regular identifiers and delimited identifiers.
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## Regular identifiers
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A regular identifier is a string of characters that starts with an ASCII letter (lower or upper case).
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The next character can either be a letter, digit, or underscore (_). It can't be a reserved keyword.
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Whitespace and other special characters are also not allowed.
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OpenSearch supports the following regular identifiers:
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1. Identifiers prefixed by a dot `.` sign. Use to hide an index. For example `.opensearch-dashboards`.
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2. Identifiers prefixed by an `@` sign. Use for meta fields generated by Logstash ingestion.
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3. Identifiers with hyphen `-` in the middle. Use for index names with date information.
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4. Identifiers with star `*` present. Use for wildcard match of index patterns.
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For regular identifiers, you can use the name without any back tick or escape characters.
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In this example, `source`, `fields`, `account_number`, `firstname`, and `lastname` are all identifiers. Out of these, the `source` field is a reserved identifier.
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```sql
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source=accounts | fields account_number, firstname, lastname;
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```
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| account_number | firstname | lastname |
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:--- | :--- |
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| 1 | Amber | Duke
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| 6 | Hattie | Bond
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| 13 | Nanette | Bates
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| 18 | Dale | Adams
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## Delimited identifiers
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A delimited identifier can contain special characters not allowed by a regular identifier.
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You must enclose delimited identifiers with back ticks (\`\`). Back ticks differentiate the identifier from special characters.
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If the index name includes a dot (`.`), for example, `log-2021.01.11`, use delimited identifiers with back ticks to escape it \``log-2021.01.11`\`.
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Typical examples of using delimited identifiers:
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1. Identifiers with reserved keywords.
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2. Identifiers with a `.` present. Similarly, `-` to include date information.
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3. Identifiers with other special characters. For example, Unicode characters.
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To quote an index name with back ticks:
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```sql
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source=`accounts` | fields `account_number`;
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```
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| account_number |
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:--- |
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## Case sensitivity
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Identifiers are case sensitive. They must be exactly the same as what's stored in OpenSearch.
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For example, if you run `source=Accounts`, you'll get an index not found exception because the actual index name is in lower case.
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