DAYNAME
描述
DAYNAME 函数用于计算日期或时间表达式对应的星期名称（如“Tuesday” 等），返回值为字符串类型。
可以通过会话变量 lc_time_names 设置输出结果的语言，该变量默认为 en_US，即输出英文。
该函数与 mysql 中的 dayname 函数 行为一致
语法
DAYNAME(<date_or_time_expr>)
参数
| 参数 | 说明 |
|---|---|
<date_or_time_expr> | 参数是合法的日期表达式，支持输入 date/datetime 类型和符合日期时间格式的字符串,具体 datetime 和 date 格式请查看 datetime 的转换 和 date 的转换 |
返回值
返回日期对应的星期名称（字符串类型）
特殊情况：
- 若
date_or_time_expr为 NULL，返回 NULL；
举例
-- 计算 DATETIME 类型对应的星期名称
select dayname('2007-02-03 00:00:00');
+--------------------------------+
| dayname('2007-02-03 00:00:00') |
+--------------------------------+
| Saturday |
+--------------------------------+
-- 计算 DATE 类型对应的星期名称
select dayname('2023-10-01');
+-----------------------+
| dayname('2023-10-01') |
+-----------------------+
| Sunday |
+-----------------------+
---参数为 NULL，返回 NULL
select dayname(NULL);
+---------------+
| dayname(NULL) |
+---------------+
| NULL |
+---------------+
---通过设置 `lc_time_namse` 控制输出语言
SET lc_time_names='zh_CN';
select dayname('2023-10-01');
+-----------------------+
| dayname('2023-10-01') |
+-----------------------+
| 星期日 |
+-----------------------+
SET lc_time_names='ar_ae';
select dayname('2023-10-01');
+-----------------------+
| dayname('2023-10-01') |
+-----------------------+
| الأحد |
+-----------------------+
附表：lc_time_names 支持的语言地区代码(不区分大小写)
| Locale Value | Meaning |
|---|---|
| ar_AE | Arabic - United Arab Emirates |
| ar_BH | Arabic - Bahrain |
| ar_DZ | Arabic - Algeria |
| ar_EG | Arabic - Egypt |
| ar_IN | Arabic - India |
| ar_IQ | Arabic - Iraq |
| ar_JO | Arabic - Jordan |
| ar_KW | Arabic - Kuwait |
| ar_LB | Arabic - Lebanon |
| ar_LY | Arabic - Libya |
| ar_MA | Arabic - Morocco |
| ar_OM | Arabic - Oman |
| ar_QA | Arabic - Qatar |
| ar_SA | Arabic - Saudi Arabia |
| ar_SD | Arabic - Sudan |
| ar_SY | Arabic - Syria |
| ar_TN | Arabic - Tunisia |
| ar_YE | Arabic - Yemen |
| be_BY | Belarusian - Belarus |
| bg_BG | Bulgarian - Bulgaria |
| ca_ES | Catalan - Spain |
| cs_CZ | Czech - Czech Republic |
| da_DK | Danish - Denmark |
| de_AT | German - Austria |
| de_BE | German - Belgium |
| de_CH | German - Switzerland |
| de_DE | German - Germany |
| de_LU | German - Luxembourg |
| el_GR | Greek - Greece |
| en_AU | English - Australia |
| en_CA | English - Canada |
| en_GB | English - United Kingdom |
| en_IN | English - India |
| en_NZ | English - New Zealand |
| en_PH | English - Philippines |
| en_US | English - United States |
| en_ZA | English - South Africa |
| en_ZW | English - Zimbabwe |
| es_AR | Spanish - Argentina |
| es_BO | Spanish - Bolivia |
| es_CL | Spanish - Chile |
| es_CO | Spanish - Colombia |
| es_CR | Spanish - Costa Rica |
| es_DO | Spanish - Dominican Republic |
| es_EC | Spanish - Ecuador |
| es_ES | Spanish - Spain |
| es_GT | Spanish - Guatemala |
| es_HN | Spanish - Honduras |
| es_MX | Spanish - Mexico |
| es_NI | Spanish - Nicaragua |
| es_PA | Spanish - Panama |
| es_PE | Spanish - Peru |
| es_PR | Spanish - Puerto Rico |
| es_PY | Spanish - Paraguay |
| es_SV | Spanish - El Salvador |
| es_US | Spanish - United States |
| es_UY | Spanish - Uruguay |
| es_VE | Spanish - Venezuela |
| et_EE | Estonian - Estonia |
| eu_ES | Basque - Spain |
| fi_FI | Finnish - Finland |
| fo_FO | Faroese - Faroe Islands |
| fr_BE | French - Belgium |
| fr_CA | French - Canada |
| fr_CH | French - Switzerland |
| fr_FR | French - France |
| fr_LU | French - Luxembourg |
| gl_ES | Galician - Spain |
| gu_IN | Gujarati - India |
| he_IL | Hebrew - Israel |
| hi_IN | Hindi - India |
| hr_HR | Croatian - Croatia |
| hu_HU | Hungarian - Hungary |
| id_ID | Indonesian - Indonesia |
| is_IS | Icelandic - Iceland |
| it_CH | Italian - Switzerland |
| it_IT | Italian - Italy |
| ja_JP | Japanese - Japan |
| ko_KR | Korean - Republic of Korea |
| lt_LT | Lithuanian - Lithuania |
| lv_LV | Latvian - Latvia |
| mk_MK | Macedonian - North Macedonia |
| mn_MN | Mongolia - Mongolian |
| ms_MY | Malay - Malaysia |
| nb_NO | Norwegian(Bokmål) - Norway |
| nl_BE | Dutch - Belgium |
| nl_NL | Dutch - The Netherlands |
| no_NO | Norwegian - Norway |
| pl_PL | Polish - Poland |
| pt_BR | Portugese - Brazil |
| pt_PT | Portugese - Portugal |
| rm_CH | Romansh - Switzerland |
| ro_RO | Romanian - Romania |
| ru_RU | Russian - Russia |
| ru_UA | Russian - Ukraine |
| sk_SK | Slovak - Slovakia |
| sl_SI | Slovenian - Slovenia |
| sq_AL | Albanian - Albania |
| sr_RS | Serbian - Serbia |
| sv_FI | Swedish - Finland |
| sv_SE | Swedish - Sweden |
| ta_IN | Tamil - India |
| te_IN | Telugu - India |
| th_TH | Thai - Thailand |
| tr_TR | Turkish - Turkey |
| uk_UA | Ukrainian - Ukraine |
| ur_PK | Urdu - Pakistan |
| vi_VN | Vietnamese - Vietnam |
| zh_CN | Chinese - China |
| zh_HK | Chinese - Hong Kong |
| zh_TW | Chinese - Taiwan |
