How to Extract Text from Oracle BLOBs?

Oracle SQL: Retrieving Textual Content from BLOBs

When working with Oracle BLOBs (Binary Large Objects), you may encounter situations where you need to extract textual content for analysis or display. By default, querying a BLOB field without specific casting will only return an object reference.

Querying Textual Content from BLOBs

To retrieve the textual content of a BLOB, you can use the following query:

select utl_raw.cast_to_varchar2(dbms_lob.substr(BLOB_FIELD))
from TABLE_WITH_BLOB
where ID = '<row id>';</row>

Explanation:

• dbms_lob.substr(BLOB_FIELD): This function extracts a substring from the BLOB starting from the first character. The result is a RAW data type.
• utl_raw.cast_to_varchar2(RAW_DATA): This function converts the RAW data to a VARCHAR2 string, allowing it to be displayed or stored in a character column.

Considerations:

• The query only retrieves the first 32767 characters of the BLOB. If the BLOB contains more text, you can increase the number inside the substr function.
• Ensure compatibility between the character sets of the BLOB data, database, and VARCHAR2 string. Otherwise, character conversion errors may occur.

Alternative for Text Storage:

It's worth noting that BLOBs are primarily designed for binary data. For storing textual content, consider using CLOBs (Character Large Objects) or NCLOBs (National Character Large Objects), which are specifically optimized for storing large amounts of textual data.

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