In Databricks Runtime 7.3 LTS, merge supports schema evolution of only top-level columns, and not of nested columns.Case is preserved when appending a new column. The added columns are appended to the end of the struct they are present in. When both options are specified, the option from the DataFrameWriter takes precedence. withColumnRenamed("dateOfBirth", "birthDate")Ĭolumns that are present in the DataFrame but missing from the table are automatically added as part of a write transaction when: ![]() The following example shows changing a column name: ((.) withColumn("birthDate", col("birthDate").cast("date")) The following example shows changing a column type: ((.) To do this, use the overwriteSchema option. You can change a column’s type or name or drop a column by rewriting the table. To drop multiple columns: ALTER TABLE table_name DROP COLUMNS (col_name_1, col_name_2)Įxplicitly update schema to change column type or name To drop a column: ALTER TABLE table_name DROP COLUMN col_name You can then use VACUUM to physically delete the files that contain the dropped column data. To purge the dropped column data, you can use REORG TABLE to rewrite files. )įor example, when running the following DDL: ALTER TABLE boxes REPLACE COLUMNS (colC STRING, colB STRUCT, colA STRING)Įxplicitly update schema to rename columnsĭropping a column from metadata does not delete the underlying data for the column in files. To change a column in a nested field, use: ALTER TABLE table_name ALTER col_name.nested_col_name (COMMENT col_comment | FIRST | AFTER colA_name)įor example, if the schema before running ALTER TABLE boxes ALTER COLUMN colB.field2 FIRST is: - rootĮxplicitly update schema to replace columns ALTER TABLE table_name REPLACE COLUMNS (col_name1 col_type1. Explicitly update schema to change column comment or ordering ALTER TABLE table_name ALTER col_name (COMMENT col_comment | FIRST | AFTER colA_name) The following Oracle ALTER TABLE statement would drop the salary column from the employees table: ALTER TABLE employeesĭROP COLUMN salary Practice Exercise #7:īased on the departments table below, rename the department_name column to dept_name.Adding nested columns is supported only for structs. State varchar2(2)) Practice Exercise #6:īased on the employees table below, drop the salary column. MODIFY (customer_name varchar2(50) NOT NULL, The following Oracle ALTER TABLE statement would modify the customer_name and state columns accordingly in the customers table: ALTER TABLE customers ![]() MODIFY employee_name varchar2(75) Practice Exercise #5:īased on the customers table below, change the customer_name column to NOT allow null values and change the state column to a varchar2(2) datatype. The following Oracle ALTER TABLE statement would change the datatype for the employee_name column to varchar2(75): ALTER TABLE employees Last_contacted date) Practice Exercise #4:īased on the employees table below, change the employee_name column to a varchar2(75) datatype. The following Oracle ALTER TABLE statement would add the contact_name and last_contacted columns to the customers table: ALTER TABLE customers CREATE TABLE customersĬONSTRAINT customers_pk PRIMARY KEY (customer_id) The following Oracle ALTER TABLE statement would add a bonus column to the employees table: ALTER TABLE employeesĪDD bonus number(6) Practice Exercise #3:īased on the customers table below, add two columns - one column called contact_name that is a varchar2(50) datatype and one column called last_contacted that is a date datatype. CREATE TABLE employeesĬONSTRAINT employees_pk PRIMARY KEY (employee_number) The following Oracle ALTER TABLE statement would rename the departments table to depts: ALTER TABLE departmentsīased on the employees table below, add a column called bonus that is a number(6) datatype. CREATE TABLE departmentsĬONSTRAINT departments_pk PRIMARY KEY (department_id) Based on the departments table below, rename the departments table to depts.
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