Hive添加或删除字段

官方文档关于Add/ReplaceColumns操作的说明

// 创建测试表
CREATE TABLE IF NOT EXISTS test (id BIGINT, name STRING);
// 插入一条数据
INSERT INTO TABLE test VALUES(2341344423,"lisi");
// 添加字段
ALTER TABLE test ADD COLUMNS(age Int);
// 插入一条数据
INSERT INTO TABLE test VALUES(2341344422,"zhangsan",18);

原有数据在新增一个或多个字段后，会将新增字段的值设置为null

在删除一个或多个字段后，原始数据的原始字段的值不会随之丢失

// 删除字段(使用新schema替换原有的)
ALTER TABLE test REPLACE COLUMNS(id BIGINT, name STRING);

修改字段（名称/类型/位置/注释）

ALTER TABLE table_name [PARTITION partition_spec] CHANGE [COLUMN] col_old_name col_new_name column_type
  [COMMENT col_comment] [FIRST|AFTER column_name] [CASCADE|RESTRICT];

• 示例

CREATE TABLE test_change (a int, b int, c int);
 
// First change column a's name to a1.
ALTER TABLE test_change CHANGE a a1 INT;
 
// Next change column a1's name to a2, its data type to string, and put it after column b.
ALTER TABLE test_change CHANGE a1 a2 STRING AFTER b;
// The new table's structure is:  b int, a2 string, c int.
  
// Then change column c's name to c1, and put it as the first column.
ALTER TABLE test_change CHANGE c c1 INT FIRST;
// The new table's structure is:  c1 int, b int, a2 string.
  
// Add a comment to column a1
ALTER TABLE test_change CHANGE a1 a1 INT COMMENT 'this is column a1';