DROP INDEX命令用于删除指定的索引。如果索引创建时未指定索引名称，则索引名称为TableName_ColumnName_idx。
语法
DROP INDEX <identifier>
或者 -
Drop index IF EXISTS KeyspaceName.IndexName
删除索引的规则
- 如果索引不存在，它将返回错误，除非您使用
IF EXISTS，否则不返回任何操作。 - 在创建索引期间，您必须使用索引名称指定
keyspace名称，否则将当前键空间中的索引删除。
示例：
下面举个例子来演示如何删除某列上的索引。在这里，我们将创建的索引放在表“student”中的“student_name”列中。键空间的名称是“yiibai_ks”。
Drop index IF EXISTS yiibai_ks.student_name_index;
如下语句 -
## 首先创建一个索引： student_name_index
cqlsh:yiibai_ks> CREATE INDEX student_name_index ON student (student_name);
cqlsh:yiibai_ks> describe student;
CREATE TABLE yiibai_ks.student (
student_id int PRIMARY KEY,
student_fees varint,
student_name text
) WITH bloom_filter_fp_chance = 0.01
AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
AND comment = ''
AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
AND crc_check_chance = 1.0
AND dclocal_read_repair_chance = 0.1
AND default_time_to_live = 0
AND gc_grace_seconds = 864000
AND max_index_interval = 2048
AND memtable_flush_period_in_ms = 0
AND min_index_interval = 128
AND read_repair_chance = 0.0
AND speculative_retry = '99PERCENTILE';
CREATE INDEX student_name_index ON yiibai_ks.student (student_name);
## 删除索引 = student_name_index
cqlsh:yiibai_ks> Drop index IF EXISTS student_name_index;
cqlsh:yiibai_ks> describe student;
CREATE TABLE yiibai_ks.student (
student_id int PRIMARY KEY,
student_fees varint,
student_name text
) WITH bloom_filter_fp_chance = 0.01
AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
AND comment = ''
AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
AND crc_check_chance = 1.0
AND dclocal_read_repair_chance = 0.1
AND default_time_to_live = 0
AND gc_grace_seconds = 864000
AND max_index_interval = 2048
AND memtable_flush_period_in_ms = 0
AND min_index_interval = 128
AND read_repair_chance = 0.0
AND speculative_retry = '99PERCENTILE';
cqlsh:yiibai_ks>
从“student_name”列中删除索引。
注意：通过再次使用 DROP 索引命令，可以验证索引是否被删除。它将显示一条消息，索引已经被删除。
cqlsh:yiibai_ks> Drop index student_name_index;
InvalidRequest: Error from server: code=2200 [Invalid query] message="Index 'student_name_index' could not be found in any of the tables of keyspace 'yiibai_ks'"
cqlsh:yiibai_ks>
