下面是我的表格和我运行的一些查询需要花费很多时间（10-40秒）。我应该添加哪些索引，以便在不使表太大的情况下提高性能。另外我被告知，如果我使用'abc％'作为我喜欢的查询，我可以使用索引。这是真的吗？
phppos_items
+-----------------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------------------+--------------+------+-----+---------+----------------+
| name | varchar(255) | NO | | NULL | |
| category | varchar(255) | NO | | NULL | |
| supplier_id | int(11) | YES | MUL | NULL | |
| item_number | varchar(255) | YES | UNI | NULL | |
| description | varchar(255) | NO | | NULL | |
| cost_price | double(15,2) | NO | | NULL | |
| unit_price | double(15,2) | NO | | NULL | |
| quantity | double(15,2) | NO | | 0.00 | |
| reorder_level | double(15,2) | NO | | 0.00 | |
| location | varchar(255) | NO | | NULL | |
| item_id | int(10) | NO | PRI | NULL | auto_increment |
| allow_alt_description | tinyint(1) | NO | | NULL | |
| is_serialized | tinyint(1) | NO | | NULL | |
| deleted | int(1) | NO | | 0 | |
+-----------------------+--------------+------+-----+---------+----------------+
#checking if item exists
SELECT * FROM (`phppos_items`) WHERE `item_id` = 1
#Get all offset + limit, can take 20+ seconds, take longer as offset gets bigger
SELECT * FROM (`phppos_items`) WHERE `deleted` = 0 ORDER BY `name` asc LIMIT 16, 16
#Count all non deleted, haven't tested yet bug I would imagine it would take awhile as deleted is not indexed
SELECT * FROM (`phppos_items`) WHERE `deleted` = 0
#Filtering, haven't tested yet, but I would guess it would take a while as there are no indexes on any of these fields
SELECT * FROM (`phppos_items`) WHERE `quantity` <= reorder_level AND `is_serialized` = 1 AND `description` = '' AND `deleted` = 0 ORDER BY `name` asc
#Get info about a particular item. This is pretty fast
SELECT * FROM (`phppos_items`) WHERE `item_id` = 1
#Get info about an item based on item_number, this seems pretty fast
SELECT * FROM (`phppos_items`) WHERE `item_number` = '1234'
#Search queries, very slow
SELECT * FROM (`phppos_items`) WHERE `deleted` = 0 AND `name` LIKE '%abc%' ORDER BY `name` asc
SELECT DISTINCT `category` FROM (`phppos_items`) WHERE `deleted` = 0 AND `category` LIKE '%abc%' ORDER BY `category` asc
SELECT * FROM (`phppos_items`) WHERE `deleted` = 0 AND `item_number` LIKE '%abc%' ORDER BY `item_number` asc
SELECT * FROM (`phppos_items`) WHERE `deleted` = 0 AND `name` LIKE '%abc%' ORDER BY `name` asc
SELECT * FROM (`phppos_items`) WHERE `deleted` = 0 AND `item_number` LIKE '%abc%' ORDER BY `item_number` asc
SELECT * FROM (`phppos_items`) WHERE (name LIKE '%abc%' or item_number LIKE '%abc%' or category LIKE '%abc%') and deleted=0 ORDER BY `name` asc LIMIT 16
#Category search, pretty fast
SELECT DISTINCT `category` FROM (`phppos_items`) WHERE `deleted` = 0 AND `category` LIKE '%abc%' ORDER BY `category` asc
#Get Categories, pretty fast
SELECT DISTINCT `category` FROM (`phppos_items`) WHERE `deleted` = 0 ORDER BY `category` asc
答案 0 :(得分：4)
您的搜索查询根本没有使用任何索引，也无法使用当前查询的索引。
如果您执行like '%....%'，则无法使用索引。
您的选择是：
like '...%' 至于您的limit / offset问题。
请尝试使用offset之类的内容，而不要使用name > 'previous name'。虽然name是唯一的，但类似的东西才能正常工作。通常，您永远不想使用超过1000的limit / offset，因为数据库必须遍历所有这些行。
答案 1 :(得分：3)
一般的经验法则是查看WHERE子句并索引其中使用的列。查看您拥有的第一批候选人将为deleted和item_number添加索引。 MySQL将为您提供主键索引。 SHOW INDEX将显示表的索引信息。
关于在LIKE参数的开头没有通配符的说法是正确的。看一下这个question。为字符串构建INDEX的方法是从开始到结束查看字符串并将其插入到索引中。从您的查询看起来，您可能需要查看FULLTEXT索引或可能重新处理问题，因此您不必创建FULLTEXT索引。
答案 2 :(得分：1)
另一个好的经验法则是永远不要使用
select *
在一个非平凡的查询中。而是列出您需要的列。
如果您只检查是否存在行，则可以使用
select count(*)