database

问题 I have lots of tables and lots of relationships between them. When I try to make some join between them I'm stuck at finding the relationship between the two tables. For the sake of simplicity let's say I have Table A and Table B . They are linked with a foreign key. Q: How can I find the foreign key between this two exact tables and the column it references? And not all the tables or foreign keys that have a reference to this table. 回答1: You can join the data dictionary constraint-related

问题 I have lots of tables and lots of relationships between them. When I try to make some join between them I'm stuck at finding the relationship between the two tables. For the sake of simplicity let's say I have Table A and Table B . They are linked with a foreign key. Q: How can I find the foreign key between this two exact tables and the column it references? And not all the tables or foreign keys that have a reference to this table. 回答1: You can join the data dictionary constraint-related

问题 I have lots of tables and lots of relationships between them. When I try to make some join between them I'm stuck at finding the relationship between the two tables. For the sake of simplicity let's say I have Table A and Table B . They are linked with a foreign key. Q: How can I find the foreign key between this two exact tables and the column it references? And not all the tables or foreign keys that have a reference to this table. 回答1: You can join the data dictionary constraint-related

问题 I have lots of tables and lots of relationships between them. When I try to make some join between them I'm stuck at finding the relationship between the two tables. For the sake of simplicity let's say I have Table A and Table B . They are linked with a foreign key. Q: How can I find the foreign key between this two exact tables and the column it references? And not all the tables or foreign keys that have a reference to this table. 回答1: You can join the data dictionary constraint-related

问题 I have lots of tables and lots of relationships between them. When I try to make some join between them I'm stuck at finding the relationship between the two tables. For the sake of simplicity let's say I have Table A and Table B . They are linked with a foreign key. Q: How can I find the foreign key between this two exact tables and the column it references? And not all the tables or foreign keys that have a reference to this table. 回答1: You can join the data dictionary constraint-related

问题 How do I determine the functional dependency and the candidate key based on this case study? Course module and it can be performed by lecturer, student or visitor user. Course module consist of subject code and subject name. When admin creates course, it will store course ID, subject code, lecturer ID, course name, and ..... Students are required to enroll in the course and the course enrollment consist of registration ID, student information, date of enrollment, date of completion and....

问题 I have function that will return all of rows, but I expect 0 or 1 because Sid is unique: CREATE DEFINER=`root`@`localhost` FUNCTION `IsInDatabase`(sId VARCHAR(21)) RETURNS tinyint(1) BEGIN RETURN (SELECT COUNT(Id) FROM table WHERE SId =sid); END When executed directly, SELECT COUNT(Id) FROM table WHERE SId ='87882118' will return exactly what I need: '1' or '0'. Why is my function not working properly ? 回答1: It's because MySQL is not case sensitive and so SId and sid are the same name, and it

问题 I have function that will return all of rows, but I expect 0 or 1 because Sid is unique: CREATE DEFINER=`root`@`localhost` FUNCTION `IsInDatabase`(sId VARCHAR(21)) RETURNS tinyint(1) BEGIN RETURN (SELECT COUNT(Id) FROM table WHERE SId =sid); END When executed directly, SELECT COUNT(Id) FROM table WHERE SId ='87882118' will return exactly what I need: '1' or '0'. Why is my function not working properly ? 回答1: It's because MySQL is not case sensitive and so SId and sid are the same name, and it

问题 I'd like to split the diamonds data frame into a list of 5 dataframe, group by cut . This instruction got me started. https://dplyr.tidyverse.org/reference/group_split.html diamonds_g <- diamonds%>% group_split(cut)%>% setNames(unique(diamonds$cut)) My desired output is a list of 5 nested lists. Each nested list contains one data frame and one matrix, such that: View(diamonds_g[[1]]) factors <- diamonds_g[[1]][2:4] mat <- diamonds_g[[1]][6:10] So each of the nested list (or each cut )

问题 I am stuck with the installation of TPC-E EGen on Mac OS X (or Linux). I have downloaded the workload generator from TPC website : www.tpc.org/tpce/egen-download-request.asp but I failed to build it. When using the following command for building the utilities: cd Utilities/prj/GNUMake/ make I receive the following error: ../../prj/GNUMake/Makefile.EGenUtilities:136: ../../obj/DateTime.d: No such file or directory ../../prj/GNUMake/Makefile.EGenUtilities:136: ../../obj/EGenVersion.d: No such