DROP INDEX命令用于刪除指定的索引。 如果索引創(chuàng)建時(shí)未指定索引名稱，則索引名稱為TableName_ColumnName_idx。

語(yǔ)法

DROP INDEX <identifier>

或者 -

Drop index IF EXISTS KeyspaceName.IndexName

刪除索引的規(guī)則

• 如果索引不存在，它將返回錯(cuò)誤，除非您使用IF EXISTS，否則不返回任何操作。
• 在創(chuàng)建索引期間，您必須使用索引名稱指定keyspace名稱，否則將當(dāng)前鍵空間中的索引刪除。

示例：

下面舉個(gè)例子來(lái)演示如何刪除某列上的索引。 在這里，我們將創(chuàng)建的索引放在表“student”中的“student_name”列中。鍵空間的名稱是“yiibai_ks”。

Drop index IF EXISTS yiibai_ks.student_name_index;

如下語(yǔ)句 -

## 首先創(chuàng)建一個(gè)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);

## 刪除索引 = 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>

從“student_name”列中刪除索引。

注意：通過(guò)再次使用DROP索引命令，可以驗(yàn)證索引是否被刪除。 它將顯示一條消息，索引已經(jīng)被刪除。

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>