# Identifier Requirements¶

Unquoted object identifiers:

_my_identifier


## Double-quoted Identifiers¶

Delimited identifiers (i.e. identifiers enclosed in double quotes) are case-sensitive and can start with and contain any valid characters, including:

• Numbers

• Special characters (., ', !, @, #, $, %, ^, &, *, etc.) • Extended ASCII and non-ASCII characters • Blank spaces For example: "MyIdentifier" "my.identifier" "my identifier" "My 'Identifier'" "3rd_identifier" "$Identifier"
"идентификатор"


Important

If an object is created using a double-quoted identifier, when referenced in a query or any other SQL statement, the identifier must be specified exactly as created, including the double quotes. Failure to include the quotes might result in an Object does not exist error (or similar type of error).

Also, note that the entire identifier must be enclosed in quotes when referenced in a query/SQL statement. This is particularly important if periods (.) are used in identifiers because periods are also used in fully-qualified object names to separate each object.

For example:

"My.DB"."My.Schema"."Table.1"


## Identifier Resolution¶

By default, Snowflake applies the following rules for storing identifiers (at creation/definition time) and resolving them (in queries and other SQL statements):

• When an identifier is unquoted, it is stored and resolved in uppercase.

• When an identifier is double-quoted, it is stored and resolved exactly as entered, including case.

For example, the following four names are equivalent and all resolve to TABLENAME:

TABLENAME
tablename
tableName
TableName


In contrast, the following four names are considered to be different, unique values:

"TABLENAME"
"tablename"
"tableName"
"TableName"


If these identifiers were used to create objects of the same type (e.g. tables), they would result in the creation of four distinct objects.

## Migrating From Databases That Treat Double-Quoted Identifiers as Case-insensitive¶

In the ANSI/ISO standard for SQL, identifiers in double quotes (delimited identifiers) are treated as case-sensitive. However, some companies provide databases that treat double-quoted identifiers as case-insensitive.

If you are migrating your data and applications from one of these databases to Snowflake, those applications might use double quotes around identifiers that are intended to be case-insensitive. This can prevent Snowflake from resolving the identifiers correctly. For example, an application might use double quotes around an identifier in lowercase, and the Snowflake database has the identifier in uppercase.

To work around this limitation, Snowflake provides the QUOTED_IDENTIFIERS_IGNORE_CASE session parameter, which causes Snowflake to treat lowercase letters in double-quoted identifiers as uppercase when creating and finding objects.

See the next sections for details:

Note

Changing the value of the parameter can affect your ability to find existing objects. See Impact of Changing the Parameter for details.

### Controlling Case Using the QUOTED_IDENTIFIERS_IGNORE_CASE Parameter¶

To configure Snowflake to treat alphabetic characters in double-quoted identifiers as uppercase for the session, set the parameter to TRUE for the session. With this setting, all alphabetical characters in identifiers are stored and resolved as uppercase characters.

In other words, the following eight names are equivalent and all resolve to TABLENAME:

TABLENAME
tablename
tableName
TableName
"TABLENAME"
"tablename"
"tableName"
"TableName"


Note that the parameter has no effect on any of the limitations for unquoted identifiers with regards to numbers, extended characters, and blank spaces.

### Impact of Changing the Parameter¶

Changing the QUOTED_IDENTIFIERS_IGNORE_CASE session parameter only affects new objects and queries:

• With the default setting of FALSE, if an object is created using a double-quoted identifier with mixed case, Snowflake stores the identifier in mixed case.

• If the parameter is later changed to TRUE, Snowflake will not be able to resolve that double-quoted mixed case identifier and will not be able retrieve that object.

Tip

Due to the impact that changing the parameter can have on resolving identifiers, we highly recommend choosing the identifier resolution method early in your implementation of Snowflake. Then, have your account administrator set the parameter at the account level to enforce this resolution method by default.

Although you can override this parameter at the session level, we don’t encourage changing the parameter from the default, unless you have an explicit need to do so.

The following examples illustrate the behavior after changing the parameter from FALSE to TRUE:

-- Set the default behavior
ALTER SESSION SET QUOTED_IDENTIFIERS_IGNORE_CASE = false;

-- Create a table with a double-quoted identifier
CREATE TABLE "One" (i int);  -- stored as "One"

-- Create a table with an unquoted identifier
CREATE TABLE TWO(j int);     -- stored as "TWO"

-- These queries work
SELECT * FROM "One";         -- searches for "One"
SELECT * FROM two;           -- searched for "TWO"
SELECT * FROM "TWO";         -- searches for "TWO"

-- These queries do not work
SELECT * FROM One;           -- searches for "ONE"
SELECT * FROM "Two";         -- searches for "Two"

-- Change to the all-uppercase behavior
ALTER SESSION SET QUOTED_IDENTIFIERS_IGNORE_CASE = true;

-- Create another table with a double-quoted identifier
CREATE TABLE "Three"(k int); -- stored as "THREE"

-- These queries work
SELECT * FROM "Two";         -- searches for "TWO"
SELECT * FROM two;           -- searched for "TWO"
SELECT * FROM "TWO";         -- searches for "TWO"
SELECT * FROM "Three";       -- searches for "THREE"
SELECT * FROM three;         -- searches for "THREE"

-- This query does not work now - "One" is not retrievable
SELECT * FROM "One";         -- searches for "ONE"


Additionally, if the identifiers for two tables differ only by case, one identifier might resolve to a different table after changing the parameter:

-- Set the default behavior
ALTER SESSION SET QUOTED_IDENTIFIERS_IGNORE_CASE = false;

-- Create a table with a double-quoted identifier
CREATE TABLE "Tab" (i int);  -- stored as "Tab"

-- Create a table with an unquoted identifier
CREATE TABLE TAB(j int);     -- stored as "TAB"

-- This query retrieves "Tab"
SELECT * FROM "Tab";         -- searches for "Tab"

-- Change to the all-uppercase behavior
ALTER SESSION SET QUOTED_IDENTIFIERS_IGNORE_CASE = true;

-- This query retrieves "TAB"
SELECT * FROM "Tab";         -- searches for "TAB"