Select Flashback Query

Description

Oracle

The flashback query claused in Oracle retrieves past data from a table, view, or materialized view. In Oracle, the uses can include:

• Restoring deleted data or undoing an incorrect commit, comparing current data with the corresponding data at an earlier time, checking the state of transactional data at a particular time, and reporting generation tools to past data, among others. (Oracle Flashback query documentation).

Snowflake

The equivalent mechanism in Snowflake to query data from the past is the AT | BEGIN query. Notice that the only equivalent is for the AS OF statements.

Furthermore, Snowflake has complete "Time Travel" documentation that allows querying data to clone objects such as tables, views, and schemas. There are limitations on the days to access the past or deleted data (90 days before passing to Fail-safe status). For more information, review the Snowflake Time Travel Documentation.

Oracle syntax

{ VERSIONS BETWEEN
  { SCN | TIMESTAMP }
  { expr | MINVALUE } AND { expr | MAXVALUE }
| AS OF { SCN | TIMESTAMP } expr
}

Snowflake Syntax

SELECT ...
FROM ...
  {
   AT( { TIMESTAMP => <timestamp> | OFFSET => <time_difference> | STATEMENT => <id> | STREAM => '<name>' } ) |
   BEFORE( STATEMENT => <id> )
  }
[ ... ]

Notice that the query ID must reference a query executed within 14 days. If the query ID references a query over 14 days old, the following error is returned: Error: statement <query_id> not found. To work around this limitation, use the time stamp for the referenced query. (Snowflake AT | Before documentation)

Sample Source Patterns

The following data is used in the following examples to generate the query outputs.

Oracle

CREATE TABLE Employee (
    EmployeeID NUMBER PRIMARY KEY,
    FirstName VARCHAR2(50),
    LastName VARCHAR2(50),
    EmailAddress VARCHAR2(100),
    HireDate DATE,
    SalaryAmount NUMBER(10, 2)
);

INSERT INTO Employee VALUES (1, 'Bob', 'SampleNameA', '[e-mail]', TO_DATE('2023-01-15', 'YYYY-MM-DD'), 11111.00);
INSERT INTO Employee VALUES (2, 'Bob', 'SampleNameB', '[e-mail]', TO_DATE('2023-01-15', 'YYYY-MM-DD'), 11111.00);
INSERT INTO Employee VALUES (3, 'Bob', 'SampleNameC', '[e-mail]', TO_DATE('2022-03-10', 'YYYY-MM-DD'), 11111.00);
INSERT INTO Employee VALUES (4, 'Bob', 'SampleNameD', '[e-mail]', TO_DATE('2022-03-10', 'YYYY-MM-DD'), 11111.00);
INSERT INTO Employee VALUES (5, 'Bob', 'SampleNameE', '[e-mail]', TO_DATE('2022-03-10', 'YYYY-MM-DD'), 11111.00);

Snowflake

CREATE OR REPLACE TABLE Employee (
       EmployeeID NUMBER(38, 18) /*** MSC-WARNING - MSCEWI1066 - NUMBER TYPE COLUMN MAY NOT BEHAVE SIMILARLY IN SNOWFLAKE ***/ PRIMARY KEY,
       FirstName VARCHAR(50) /*** MSC-WARNING - MSCEWI1036 - VARCHAR2 DATA TYPE CONVERTED TO VARCHAR ***/,
       LastName VARCHAR(50) /*** MSC-WARNING - MSCEWI1036 - VARCHAR2 DATA TYPE CONVERTED TO VARCHAR ***/,
       EmailAddress VARCHAR(100) /*** MSC-WARNING - MSCEWI1036 - VARCHAR2 DATA TYPE CONVERTED TO VARCHAR ***/,
       HireDate TIMESTAMP /*** MSC-WARNING - MSCEWI3060 - DEFAULT VALUE FOR SYSDATE IS CURRENT_TIMESTAMP. COLUMN WAS TRANSFORMED TO TIMESTAMP TO PRESERVE INFORMATION. ***/,
       SalaryAmount NUMBER(10, 2) /*** MSC-WARNING - MSCEWI1066 - NUMBER TYPE COLUMN MAY NOT BEHAVE SIMILARLY IN SNOWFLAKE ***/
   );

   INSERT INTO Employee
   VALUES (1, 'Bob', 'SampleNameA', '[e-mail]', TO_DATE('2023-01-15', 'YYYY-MM-DD'), 11111.00);

   INSERT INTO Employee
   VALUES (2, 'Bob', 'SampleNameB', '[e-mail]', TO_DATE('2023-01-15', 'YYYY-MM-DD'), 11111.00);

   INSERT INTO Employee
   VALUES (3, 'Bob', 'SampleNameC', '[e-mail]', TO_DATE('2022-03-10', 'YYYY-MM-DD'), 11111.00);

   INSERT INTO Employee
   VALUES (4, 'Bob', 'SampleNameD', '[e-mail]', TO_DATE('2022-03-10', 'YYYY-MM-DD'), 11111.00);

   INSERT INTO Employee
   VALUES (5, 'Bob', 'SampleNameE', '[e-mail]', TO_DATE('2022-03-10', 'YYYY-MM-DD'), 11111.00);

1. AS OF with TIMESTAMP case

Oracle

Query

SELECT * FROM employees
AS OF TIMESTAMP
TO_TIMESTAMP('2023-09-27 07:00:00', 'YYYY-MM-DD HH:MI:SS')
WHERE last_name = 'SampleName';

Output

Snowflake

Query

SELECT * FROM
employees
--** MSC-WARNING - MSCEWI3135 - DATA RETENTION PERIOD MAY PRODUCE NO RESULTS **
AT (TIMESTAMP =>
TO_TIMESTAMP('2023-09-27 07:00:00', 'YYYY-MM-DD HH:MI:SS'))
WHERE last_name = 'SampleName';

Output

2. AS OF with SCN case

Oracle

Query

SELECT * FROM employees
AS OF SCN
TO_TIMESTAMP('2023-09-27 07:00:00', 'YYYY-MM-DD HH:MI:SS')
WHERE last_name = 'SampleName';

Snowflake

Query

SELECT * FROM
employees
----** MSC-WARNING - MSCEWI1040 - THE STATEMENT IS NOT SUPPORTED IN SNOWFLAKE **
--AS OF SCN
--TO_TIMESTAMP('2023-09-27 07:00:00', 'YYYY-MM-DD HH:MI:SS')
WHERE last_name = 'SampleName';

Known Issues

1. The option when it is using SCN is not supported.

2. The VERSION statement is not supported in Snowflake.

Related EWIS

MSCEWI1058: Functionality is not currently supported by Snowflake Scripting

MSCEWI3135: Data Retention Period May Produce No Results