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COMPOSE takes as its argument a string, or an expression that resolves to a string, in any data type, and returns a Unicode string in the same character set as the input. char can be any of the data types CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB. For example, an o code point qualified by an umlaut code point will be returned as the o-umlaut code point.

COMPOSE returns the string in NFC normal form. For a more exclusive setting, you can first call DECOMPOSE with the CANONICAL setting and then COMPOSE. This combination returns the string in NFKC normal form.

CLOB and NCLOB values are supported through implicit conversion. If char is a character LOB value, then it is converted to a VARCHAR value before the COMPOSE operation. The operation will fail if the size of the LOB value exceeds the supported length of the VARCHAR in the particular development environment.

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The following example returns the o-umlaut code point:

SELECT COMPOSE( 'o' || UNISTR('\0308') )


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