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>