Understanding the DELETE FROM Operation

Delete All Data from a Table

To delete all data from a HPE Ezmeral Data Fabric DatabaseJSON table use the following operator:

DELETE FROM <table_name>;

Example. In this example we create a table, insert data, and delete all rows:

DROP TABLE IF EXISTS customer;
CREATE TABLE customer(doc_id STRING, first_name STRING, last_name STRING) STORED BY 'org.apache.hadoop.hive.maprdb.json.MapRDBJsonStorageHandler'
TBLPROPERTIES("maprdb.table.name" = "/customer","maprdb.column.id" = "doc_id");
INSERT INTO TABLE customer VALUES ("001", "Max", "Born"), ("002", "Demmy", "John"), ("003", "Robby", "Smart");
SELECT doc_id, first_name, last_name FROM customer;

The following query gives an empty set. Deletions are supported only for HPE Ezmeral Data Fabric Database JSON tables and transactional tables.

DELETE FROM customer;
SELECT doc_id, first_name, last_name FROM customer;

Example. In this example, we try to delete data from a non-transactional and non-MapR Database JSON table:

DROP TABLE IF EXISTS simple_data;
CREATE TABLE simple_data (id INT);
INSERT INTO TABLE simple_data VALUES (1), (2), (3);
DELETE FROM simple_data;

The result is:

FAILED: SemanticException Operation is not supported. Table is nor ACID neither MapRDbJSON

Delete a Single Row from a Table

To delete a single row from a HPE Ezmeral Data Fabric Database JSON table, use the following syntax:

DELETE FROM <table_name> WHERE <id> = <value>;

Where:

<table_name> is the HPE Ezmeral Data Fabric Database JSON table.

<id> is a key column of the MapR Database JSON table. It corresponds to the maprdb.column.id property.

<value> is the value to be deleted.

Example. In this example, we create a table, insert data, and delete a single row:

DROP TABLE IF EXISTS customer;
CREATE TABLE customer(doc_id STRING, first_name STRING, last_name STRING) STORED BY 'org.apache.hadoop.hive.maprdb.json.MapRDBJsonStorageHandler'
TBLPROPERTIES("maprdb.table.name" = "/customer","maprdb.column.id" = "doc_id");
INSERT INTO customer VALUES ("001", "Max", "Born"), ("002", "Demmy", "John"), ("003", "Robby", "Smart");
SELECT doc_id, first_name, last_name FROM customer;

The following query deletes a single row using the WHERE clause:

DELETE FROM customer WHERE doc_id = "002";
SELECT doc_id, first_name, last_name FROM customer;

Note. Deletions are supported only for key columns of HPE Ezmeral Data Fabric Database JSON tables.

Example. In this example, we try to use a column other than a key column of the MapR Database JSON table in deletion.

DROP TABLE IF EXISTS customer;
CREATE TABLE customer(doc_id STRING, first_name STRING, last_name STRING) STORED BY 'org.apache.hadoop.hive.maprdb.json.MapRDBJsonStorageHandler'
TBLPROPERTIES("maprdb.table.name" = "/customer","maprdb.column.id" = "doc_id");
INSERT INTO customer VALUES ("001", "Max", "Born"), ("002", "Demmy", "John"), ("003", "Robby", "Smart");
SELECT doc_id, first_name, last_name FROM customer;

Column first_name is not the key column of the table.

DELETE FROM customer WHERE first_name = "Max";

The result is:

FAILED: SemanticException Deletion over column first_name is forbidden. Use only key column of MapR Db Json table: doc_id

Delete Several Rows from a Table

To delete several rows from a table, use the following syntax:

DELETE FROM <table_name> WHERE <id> IN (<value1>, <value2>, ...);

Where:

<table_name> is the HPE Ezmeral Data Fabric Database JSON table.

<id> is a key column of the MapR Database JSON table. It corresponds to the maprdb.column.id property.

<value1>, <value2>, are values to be deleted.

Example. In this example, we create a table, insert data, and delete several rows:

DROP TABLE IF EXISTS customer;
CREATE TABLE customer(doc_id STRING, first_name STRING, last_name STRING) STORED BY 'org.apache.hadoop.hive.maprdb.json.MapRDBJsonStorageHandler'
TBLPROPERTIES("maprdb.table.name" = "/customer","maprdb.column.id" = "doc_id");
INSERT INTO TABLE customer VALUES ("001", "Max", "Born"), ("002", "Demmy", "John"), ("003", "Robby", "Smart");
SELECT doc_id, first_name, last_name FROM customer;

The following query deletes several rows using the WHERE ... IN clause:

DELETE FROM customer WHERE doc_id IN ("001", "002");
SELECT doc_id, first_name, last_name FROM customer;

Delete All Rows in a Table Except Listed Rows

To delete all rows from a table except a listed row, use the following syntax:

DELETE FROM <table_name> WHERE <id> NOT IN (<value1>, <value2>, ...);

Where:

<table_name> is the HPE Ezmeral Data Fabric Database JSON table.

<id> is a key column of the MapR Database JSON table. It corresponds to the maprdb.column.id property.

<value1>, <value2>, are values to be preserved.

Example. In this example, we create a table, insert data, and delete all rows except the listed rows:

DROP TABLE IF EXISTS customer;
CREATE TABLE customer(doc_id STRING, first_name STRING, last_name STRING) STORED BY 'org.apache.hadoop.hive.maprdb.json.MapRDBJsonStorageHandler'
TBLPROPERTIES("maprdb.table.name" = "/customer","maprdb.column.id" = "doc_id");
INSERT INTO TABLE customer VALUES ("001", "Max", "Born"), ("002", "Demmy", "John"), ("003", "Robby", "Smart");
SELECT doc_id, first_name, last_name FROM customer;

The following query deletes all rows except the listed rows:

DELETE FROM customer WHERE doc_id NOT IN ("003");
SELECT doc_id, first_name, last_name FROM customer;

Limitations of the DELETE FROM Operation

The following are three limitations of the current implementation:

• The current implementation does not support arbitrary conditions in the WHERE clause of the DELETE statement even if a key column is used.

  Example. In this example, DELETE FROM is used with an arbitrary condition:

  DELETE FROM customer WHERE doc_id == "003" OR doc_id <> "005";

  The result is:

  FAILED:
          SemanticException This condition is not supported for MapR Db Json deletions. Supported
          WHERE clauses are: <id> = value, <id> IN (value1, value2, ...), <id> NOT IN (value1, value2,
          ...)

• The current implementation does not support subqueries in the WHERE clause.
• The current implementation does not support deletions in the MERGE statement.