redis命令怎么查看数据库的数量

使用命令`INFO`可以查看Redis服务器的各种信息，其中包括数据库的数量。在INFO返回的信息中，可以查找键为`"dbX"`(X为数字，表示数据库编号)的信息，每个键对应一个数据库的信息，因此可以统计`"db"`开头的键的数量即可得到数据库的数量。

示例：

127.0.0.1:6379> INFO
# Server
redis_version:5.0.5
redis_git_sha1:00000000
redis_git_dirty:0
redis_build_id:b8f43c0d84b2d1c9
redis_mode:standalone
os:Linux 4.4.0-18362-Microsoft x86_64
arch_bits:64
multiplexing_api:epoll
atomicvar_api:atomic-builtin
gcc_version:8.3.0
process_id:12151
run_id:c9df8cd171e8f7b151f72c1d1a2a6ce8987c98d9
tcp_port:6379
uptime_in_seconds:303
uptime_in_days:0
hz:10
configured_hz:10
lru_clock:14220392
executable:/usr/local/bin/redis-server
config_file:

# Clients
connected_clients:1
client_recent_max_input_buffer:2
client_recent_max_output_buffer:0
blocked_clients:0

# Memory
used_memory:870368
used_memory_human:850.00K
used_memory_rss:9076736
used_memory_rss_human:8.66M
used_memory_peak:907264
used_memory_peak_human:886.72K
used_memory_peak_perc:95.85%
used_memory_overhead:357896
used_memory_startup:784392
used_memory_dataset:512472
used_memory_dataset_perc:70.65%
allocator_allocated:1253120
allocator_active:1740800
allocator_resident:10731520
total_system_memory:1073741824
total_system_memory_human:1.00G
used_memory_lua:37888
used_memory_lua_human:37.00K
used_memory_scripts:0
used_memory_scripts_human:0B
number_of_cached_scripts:0
maxmemory:0
maxmemory_human:0B
maxmemory_policy:noeviction
allocator_frag_ratio:1.39
allocator_frag_bytes:487680
allocator_rss_ratio:6.18
allocator_rss_bytes:8990720
rss_overhead_ratio:0.84
rss_overhead_bytes:-1665024
mem_fragmentation_ratio:11.55
mem_fragmentation_bytes:8206368
mem_not_counted_for_evict:0
mem_replication_backlog:0
mem_clients_slaves:0
mem_clients_normal:0
mem_aof_buffer:0
mem_allocator:libc

# Persistence
loading:0
rdb_changes_since_last_save:0
rdb_bgsave_in_progress:0
rdb_last_save_time:1604918176
rdb_last_bgsave_status:ok
rdb_last_bgsave_time_sec:-1
rdb_current_bgsave_time_sec:-1
rdb_last_cow_size:0
aof_enabled:0
aof_rewrite_in_progress:0
aof_rewrite_scheduled:0
aof_last_rewrite_time_sec:-1
aof_current_rewrite_time_sec:-1
aof_last_bgrewrite_status:ok
aof_last_write_status:ok
aof_last_cow_size:0

# Stats
total_connections_received:3
total_commands_processed:10
instantaneous_ops_per_sec:0
total_net_input_bytes:236
total_net_output_bytes:2305
instantaneous_input_kbps:0.00
instantaneous_output_kbps:0.00
rejected_connections:0
sync_full:0
sync_partial_ok:0
sync_partial_err:0
expired_keys:0
expired_stale_perc:0.00
expired_time_cap_reached_count:0
evicted_keys:0
keyspace_hits:0
keyspace_misses:0
pubsub_channels:0
pubsub_patterns:0
latest_fork_usec:0
migrate_cached_sockets:0

# Replication
role:master
connected_slaves:0
master_replid:5c5f5d5f5d9d5d5d5d5d5d5d5d5d5d5d5d5d5d5
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:0
second_repl_offset:-1
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0

# CPU
used_cpu_sys:0.013000
used_cpu_user:0.010000
used_cpu_sys_children:0.000000
used_cpu_user_children:0.000000

# Cluster
cluster_enabled:0

# Keyspace
db0:keys=0,expires=0,avg_ttl=0

在上面的输出中，可以看到`db0`对应的信息，其中`keys`表示该数据库中键的数量。如果有多个数据库，则会有多个`dbX`的信息。