Insert and delete data
Lenses SQL allows you to utilize the ANSI SQL command to store new records into a table.
Single or multi record inserts are supported:
INSERT INTO $Table(column1[, column2, column3]) VALUES(value1[,value2, value3]) INSERT INTO $Table(column1[, column2, column3]) VALUES (value1[,value2, value3]), (value4[,value5, value6])
- $Table - The name of the table to insert the data into
- Columns - The target columns to populate with data. Adding a record does not require you to fill all the available columns. In the case of Avro stored Key, Value pairs, the user needs to make sure that a value is specified for all the required Avro fields.
- VALUES - The set of value to insert. It has to match the list of columns provided, including their data types. You can use simple constants or more complex expressions as values, like
1 + 1or
INSERT INTO customer ( _key, id , address.line , address.city , address.postcode , email) VALUES ('maria.wood','maria.wood', '698 E. Bedford Lane','Los Angeles', 90044, 'email@example.com'), ('david.green', 'david.green', '4309 S Morgan St', 'Chicago', 60609, 'firstname.lastname@example.org');
Inserting data from a SELECT
Records can be inserted from the result of SELECT statement.
The syntax is as follows:
INSERT INTO $TABLE1 SELECT */column1[,column2, ...] FROM $Table2 [WHERE $condition] [LIMIT N]
For example, to copy all the records from the customer table into customer_avro one:
INSERT INTO customer_avro SELECT * FROM customer
Deleting data in Kafka
There are two ways to delete data:
- If the topic is not compacted, then
DELETEexpects an offset to delete records up to.
-- Delete records across all partitions up to the offset 10 DELETE FROM customer WHERE _meta.offset <= 10; -- Delete records from a specific partition DELETE FROM customer WHERE _meta.offset <= 10 AND _meta.partition = 2
- If the topic is compacted, then
DELETEexpects the record
Keyto be provided. For a compacted topic a delete translates to inserting a record with the existing Key, but the Value is null. For the
customer_avrotopic (which has the compacted flag on), a delete operation for a specific customer identifier would look like this:
DELETE FROM customer_avro WHERE _key = 'andy.perez'
Deleting is an insert operation. Until the compaction takes place, there will be at least one record with the Key used earlier. The latest (or last) record will have the Value set to null.
Truncating a table
To remove all records from a table:
TRUNCATE TABLE $Table
$Table is the table name to delete all records from. This operation is only supported on non-compacted topics, which is a Kafka design restriction. To remove the data from a compacted topic, you have two options: either dropping and recreating the topic or inserting null Value records for each unique Key on the topic.
After rebuilding the
customer table to be non-compacted, the truncate can be performed as follows:
TRUNCATE TABLE customer; /* SELECT count(*) FROM customer returns 0 after the previous statement */